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/main.py

@@ -8,7 +8,7 @@ import uvicorn
 logging.basicConfig(level=logging.INFO, format="%(levelname)s:%(name)s: %(message)s")
 
 from config import settings
-from routers import chat, google_chat, nextcloud_talk
+from routers import chat, google_chat, nextcloud_talk, files
 
 
 @asynccontextmanager
@@ -23,6 +23,7 @@ app = FastAPI(title="Cortex Dispatcher", lifespan=lifespan)
 app.include_router(chat.router)
 app.include_router(google_chat.router)
 app.include_router(nextcloud_talk.router)
+app.include_router(files.router)
 app.mount("/static", StaticFiles(directory="static"), name="static")