feat(phase9): extract_content_tags_cmd Tauri wrapper

Bridges LlmEngine::extract_content_tags to the frontend with the same
spawn_blocking + PowerAssertion guard the cleanup_text command uses.
Returns a ContentTags object serialised to camelCase JSON. Errors
surface as readable strings so the frontend toast shows actionable
text on the rare grammar-bypass path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src-tauri/src/lib.rs

@@ -373,6 +373,8 @@ pub fn run() {
             commands::clipboard::copy_to_clipboard,
             // Filesystem (Phase 9 save-dialog path)
             commands::fs::write_text_file_cmd,
+            // LLM content tags (Phase 9)
+            commands::llm::extract_content_tags_cmd,
             // Paste (auto-insert at cursor)
             commands::paste::paste_text,
             commands::paste::paste_text_replacing,