Composer auto-grow (1→5 lines) + in-field attach; settings screen + persisted prefs

- Composer input starts at one line and auto-grows up to 5 lines (then scrolls),
  measured via onTextLayout; attach (paperclip) moved inside the field, right of
  the text, per the Telegram reference.

- New SettingsScreen (drawer/rail entry) for Threads + Tool detail; both now
  persist via SecureStore (Android prefs / desktop JSON).

- Add AGENTS.md; rename reference screenshot to telegram_screenshot_reference.jpg.

app/shared/src/androidMain/kotlin/iris/platform/AndroidSecureStore.kt

@@ -97,6 +97,14 @@ class AndroidSecureStore(context: Context) : SecureStore {
         get() = prefs.getString(KEY_NTFY_SERVER, "").orEmpty()
         set(value) = prefs.edit().putString(KEY_NTFY_SERVER, value).apply()
 
+    override var threadsEnabled: Boolean
+        get() = prefs.getBoolean(KEY_THREADS_ENABLED, false)
+        set(value) = prefs.edit().putBoolean(KEY_THREADS_ENABLED, value).apply()
+
+    override var toolDetail: String
+        get() = prefs.getString(KEY_TOOL_DETAIL, "truncated").orEmpty().ifBlank { "truncated" }
+        set(value) = prefs.edit().putString(KEY_TOOL_DETAIL, value).apply()
+
     override fun savePairing(url: String, token: String) {
         serverUrl = url
         this.token = token
@@ -116,5 +124,7 @@ class AndroidSecureStore(context: Context) : SecureStore {
         const val KEY_FCM_TOKEN = "fcm_token"
         const val KEY_NTFY_TOPIC = "ntfy_topic"
         const val KEY_NTFY_SERVER = "ntfy_server"
+        const val KEY_THREADS_ENABLED = "threads_enabled"
+        const val KEY_TOOL_DETAIL = "tool_detail"
     }
 }