Add SSE real-time Talk activity, file editor UI, and identity file API

- event_bus.py: in-process asyncio pub/sub (one Queue per SSE client)
- nextcloud_talk.py: publishes nct_message/nct_response events to bus
- chat.py: GET /events SSE endpoint streams Talk activity to browser
- routers/files.py: whitelist-protected GET/PUT for Inara identity .md files
- main.py: register files router
- static/index.html: real-time Talk feed, blue badge on Sessions btn,
  Files modal with preview/edit toggle and Ctrl+S save

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

cortex/routers/nextcloud_talk.py

@@ -13,6 +13,7 @@ from context_loader import load_context
 from llm_client import complete
 from session_logger import log_turn
 from session_store import load as load_session, save as save_session
+import event_bus
 
 logger = logging.getLogger(__name__)
 logger.setLevel(logging.DEBUG)
@@ -78,6 +79,14 @@ async def _process_message(conversation_token: str, user_text: str, actor_name:
     history       = load_session(session_id)
     history.append({"role": "user", "content": user_text})
 
+    await event_bus.publish({
+        "type": "nct_message",
+        "session_id": session_id,
+        "role": "user",
+        "content": user_text,
+        "actor": actor_name,
+    })
+
     try:
         response_text, backend = await asyncio.wait_for(
             complete(system_prompt=system_prompt, messages=history),
@@ -96,6 +105,15 @@ async def _process_message(conversation_token: str, user_text: str, actor_name:
     history.append({"role": "assistant", "content": response_text})
     save_session(session_id, history)
     log_turn(session_id, user_text, response_text)
+
+    await event_bus.publish({
+        "type": "nct_response",
+        "session_id": session_id,
+        "role": "assistant",
+        "content": response_text,
+        "backend": backend,
+    })
+
     await _send_reply(conversation_token, response_text)