feat: display file attachments in Feed and Detail screens

- Extend FeedPost with fileUrl and fileName fields
- Parse mobiledoc file cards in FeedViewModel.extractFileCardFromMobiledoc()
- Map LocalPost file fields to FeedPost in toFeedPost()
- Create FileAttachmentCard composable with file type icon colors and tap-to-download
- Integrate file card into PostCardContent (FeedScreen) and DetailScreen

app/src/main/java/com/swoosh/microblog/data/model/GhostModels.kt

@@ -143,7 +143,9 @@ data class FeedPost(
     val createdAt: String?,
     val updatedAt: String?,
     val isLocal: Boolean = false,
-    val queueStatus: QueueStatus = QueueStatus.NONE
+    val queueStatus: QueueStatus = QueueStatus.NONE,
+    val fileUrl: String? = null,
+    val fileName: String? = null
 )
 
 @Stable

app/src/main/java/com/swoosh/microblog/ui/detail/DetailScreen.kt

@@ -54,6 +54,7 @@ import com.swoosh.microblog.data.model.PostStats
 import com.swoosh.microblog.data.model.QueueStatus
 import com.swoosh.microblog.ui.animation.SwooshMotion
 import com.swoosh.microblog.ui.components.ConfirmationDialog
+import com.swoosh.microblog.ui.feed.FileAttachmentCard
 import com.swoosh.microblog.ui.feed.FullScreenGallery
 import com.swoosh.microblog.ui.feed.StatusBadge
 import com.swoosh.microblog.ui.feed.formatRelativeTime
@@ -348,6 +349,22 @@ fun DetailScreen(
                 }
             }
 
+            // File attachment
+            if (post.fileUrl != null) {
+                AnimatedVisibility(
+                    visible = sectionVisible[4].value,
+                    enter = fadeIn(SwooshMotion.quick()) + slideInVertically(initialOffsetY = { 20 }, animationSpec = SwooshMotion.gentle())
+                ) {
+                    Column {
+                        Spacer(modifier = Modifier.height(16.dp))
+                        FileAttachmentCard(
+                            fileUrl = post.fileUrl,
+                            fileName = post.fileName ?: "File"
+                        )
+                    }
+                }
+            }
+
             // Section 5 — PostStatsSection
             AnimatedVisibility(
                 visible = sectionVisible[5].value,

app/src/main/java/com/swoosh/microblog/ui/feed/FeedScreen.kt

@@ -75,6 +75,7 @@ import androidx.compose.ui.text.withStyle
 import androidx.compose.ui.unit.DpOffset
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
+import android.content.Intent
 import androidx.compose.ui.window.Dialog
 import androidx.compose.ui.window.DialogProperties
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
@@ -1591,6 +1592,15 @@ fun PostCardContent(
                 }
             }
 
+            // File attachment
+            if (post.fileUrl != null) {
+                Spacer(modifier = Modifier.height(12.dp))
+                FileAttachmentCard(
+                    fileUrl = post.fileUrl,
+                    fileName = post.fileName ?: "File"
+                )
+            }
+
             // Tags display
             if (post.tags.isNotEmpty()) {
                 Spacer(modifier = Modifier.height(10.dp))
@@ -2176,3 +2186,73 @@ fun StatusBadge(post: FeedPost) {
         border = null
     )
 }
+
+/**
+ * Returns an appropriate icon tint color based on file extension.
+ */
+@Composable
+private fun fileTypeColorFromName(fileName: String): Color {
+    val lower = fileName.lowercase()
+    return when {
+        lower.endsWith(".pdf") -> Color(0xFFD32F2F)             // red
+        lower.endsWith(".doc") || lower.endsWith(".docx") -> Color(0xFF1565C0) // blue
+        lower.endsWith(".txt") || lower.endsWith(".csv") -> Color(0xFF757575) // gray
+        lower.endsWith(".xls") || lower.endsWith(".xlsx") -> Color(0xFF2E7D32) // green
+        lower.endsWith(".ppt") || lower.endsWith(".pptx") -> Color(0xFFE65100) // orange
+        lower.endsWith(".zip") || lower.endsWith(".rar") || lower.endsWith(".gz") -> Color(0xFF6A1B9A) // purple
+        else -> MaterialTheme.colorScheme.onSurfaceVariant
+    }
+}
+
+/**
+ * Card displaying a file attachment in Feed/Detail screens.
+ * Tapping opens the file URL in an external viewer.
+ */
+@Composable
+fun FileAttachmentCard(
+    fileUrl: String,
+    fileName: String
+) {
+    val context = LocalContext.current
+    val iconTint = fileTypeColorFromName(fileName)
+
+    OutlinedCard(
+        onClick = {
+            try {
+                val intent = Intent(Intent.ACTION_VIEW, android.net.Uri.parse(fileUrl))
+                context.startActivity(intent)
+            } catch (_: Exception) {
+                // No handler available for this file type
+            }
+        },
+        modifier = Modifier.fillMaxWidth()
+    ) {
+        Row(
+            modifier = Modifier
+                .fillMaxWidth()
+                .padding(12.dp),
+            verticalAlignment = Alignment.CenterVertically
+        ) {
+            Icon(
+                Icons.Default.InsertDriveFile,
+                contentDescription = "File attachment",
+                modifier = Modifier.size(28.dp),
+                tint = iconTint
+            )
+            Spacer(modifier = Modifier.width(12.dp))
+            Column(modifier = Modifier.weight(1f)) {
+                Text(
+                    text = fileName,
+                    style = MaterialTheme.typography.bodyMedium,
+                    maxLines = 1,
+                    overflow = TextOverflow.Ellipsis
+                )
+                Text(
+                    text = "Tap to download",
+                    style = MaterialTheme.typography.labelSmall,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant
+                )
+            }
+        }
+    }
+}

app/src/main/java/com/swoosh/microblog/ui/feed/FeedViewModel.kt

@@ -535,6 +535,7 @@ class FeedViewModel(application: Application) : AndroidViewModel(application) {
                 allImages.add(url)
             }
         }
+        val fileData = extractFileCardFromMobiledoc(mobiledoc)
         return FeedPost(
             ghostId = id,
             slug = slug,
@@ -555,7 +556,9 @@ class FeedViewModel(application: Application) : AndroidViewModel(application) {
             publishedAt = published_at,
             createdAt = created_at,
             updatedAt = updated_at,
-            isLocal = false
+            isLocal = false,
+            fileUrl = fileData?.first,
+            fileName = fileData?.second
         )
     }
 
@@ -580,6 +583,31 @@ class FeedViewModel(application: Application) : AndroidViewModel(application) {
         }
     }
 
+    /**
+     * Extracts file card data from Ghost mobiledoc JSON.
+     * File cards have the format: ["file", {"src": "url", "fileName": "name"}]
+     * Returns a Pair of (fileUrl, fileName) or null if no file card.
+     */
+    private fun extractFileCardFromMobiledoc(mobiledoc: String?): Pair<String, String>? {
+        if (mobiledoc == null) return null
+        return try {
+            val json = com.google.gson.JsonParser.parseString(mobiledoc).asJsonObject
+            val cards = json.getAsJsonArray("cards") ?: return null
+            for (card in cards) {
+                val cardArray = card.asJsonArray
+                if (cardArray.size() >= 2 && cardArray[0].asString == "file") {
+                    val cardData = cardArray[1].asJsonObject
+                    val src = cardData.get("src")?.asString ?: continue
+                    val name = cardData.get("fileName")?.asString ?: "file"
+                    return Pair(src, name)
+                }
+            }
+            null
+        } catch (e: Exception) {
+            null
+        }
+    }
+
     private fun LocalPost.toFeedPost(): FeedPost {
         val tagNames: List<String> = try {
             Gson().fromJson(tags, object : TypeToken<List<String>>() {}.type) ?: emptyList()
@@ -615,7 +643,9 @@ class FeedViewModel(application: Application) : AndroidViewModel(application) {
             createdAt = null,
             updatedAt = null,
             isLocal = true,
-            queueStatus = queueStatus
+            queueStatus = queueStatus,
+            fileUrl = uploadedFileUrl ?: fileUri,
+            fileName = fileName
         )
     }