feat: implement Phase 11 — inline photo viewing with ratatui-image

Add feature-gated (`images`) inline photo support:
- New types: MediaInfo, PhotoInfo, PhotoDownloadState, ImagesConfig
- Media module: ImageCache (LRU filesystem cache), ImageRenderer (terminal protocol detection)
- Photo metadata extraction from TDLib MessagePhoto with download_file() API
- ViewImage command (v/м) to toggle photo expand/collapse in message selection
- Two-pass UI rendering: placeholder lines in message bubbles + StatefulImage overlay
- Collapse all expanded photos on Esc (exit selection mode)

Dependencies: ratatui-image 8.1, image 0.25 (optional, behind `images` feature flag)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/helpers/fake_tdclient_impl.rs

@@ -161,6 +161,11 @@ impl TdClientTrait for FakeTdClient {
         FakeTdClient::toggle_reaction(self, chat_id, message_id, reaction).await
     }
 
+    // ============ File methods ============
+    async fn download_file(&self, file_id: i32) -> Result<String, String> {
+        FakeTdClient::download_file(self, file_id).await
+    }
+
     // ============ Getters (immutable) ============
     fn client_id(&self) -> i32 {
         0 // Fake client ID