feat: add TagRepository for tag CRUD operations

Follows PostRepository pattern: constructor takes Context, creates
AccountManager, uses ApiClient.getService, wraps calls in
withContext(Dispatchers.IO), returns Result<T>.

app/src/main/java/com/swoosh/microblog/data/repository/TagRepository.kt

@@ -0,0 +1,86 @@
+package com.swoosh.microblog.data.repository
+
+import android.content.Context
+import com.swoosh.microblog.data.AccountManager
+import com.swoosh.microblog.data.api.ApiClient
+import com.swoosh.microblog.data.api.GhostApiService
+import com.swoosh.microblog.data.model.GhostTagFull
+import com.swoosh.microblog.data.model.TagWrapper
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.withContext
+
+class TagRepository(private val context: Context) {
+
+    private val accountManager = AccountManager(context)
+
+    private fun getApi(): GhostApiService {
+        val account = accountManager.getActiveAccount()
+            ?: throw IllegalStateException("No active account configured")
+        return ApiClient.getService(account.blogUrl) { account.apiKey }
+    }
+
+    suspend fun fetchTags(): Result<List<GhostTagFull>> =
+        withContext(Dispatchers.IO) {
+            try {
+                val response = getApi().getTags()
+                if (response.isSuccessful) {
+                    Result.success(response.body()!!.tags)
+                } else {
+                    Result.failure(Exception("API error ${response.code()}: ${response.errorBody()?.string()}"))
+                }
+            } catch (e: Exception) {
+                Result.failure(e)
+            }
+        }
+
+    suspend fun createTag(
+        name: String,
+        description: String? = null,
+        accentColor: String? = null
+    ): Result<GhostTagFull> =
+        withContext(Dispatchers.IO) {
+            try {
+                val tag = GhostTagFull(
+                    name = name,
+                    description = description,
+                    accent_color = accentColor
+                )
+                val response = getApi().createTag(TagWrapper(listOf(tag)))
+                if (response.isSuccessful) {
+                    Result.success(response.body()!!.tags.first())
+                } else {
+                    Result.failure(Exception("Create tag failed ${response.code()}: ${response.errorBody()?.string()}"))
+                }
+            } catch (e: Exception) {
+                Result.failure(e)
+            }
+        }
+
+    suspend fun updateTag(id: String, tag: GhostTagFull): Result<GhostTagFull> =
+        withContext(Dispatchers.IO) {
+            try {
+                val response = getApi().updateTag(id, TagWrapper(listOf(tag)))
+                if (response.isSuccessful) {
+                    Result.success(response.body()!!.tags.first())
+                } else {
+                    Result.failure(Exception("Update tag failed ${response.code()}: ${response.errorBody()?.string()}"))
+                }
+            } catch (e: Exception) {
+                Result.failure(e)
+            }
+        }
+
+    suspend fun deleteTag(id: String): Result<Unit> =
+        withContext(Dispatchers.IO) {
+            try {
+                val response = getApi().deleteTag(id)
+                if (response.isSuccessful) {
+                    Result.success(Unit)
+                } else {
+                    Result.failure(Exception("Delete tag failed ${response.code()}"))
+                }
+            } catch (e: Exception) {
+                Result.failure(e)
+            }
+        }
+}