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/event_bus.py

@@ -0,0 +1,33 @@
+"""
+Simple in-process pub/sub for server-sent events.
+
+Usage:
+    # Publisher (e.g. nextcloud_talk router)
+    await event_bus.publish({"type": "nct_message", ...})
+
+    # Consumer (SSE endpoint in chat router)
+    q = event_bus.subscribe()
+    try:
+        event = await asyncio.wait_for(q.get(), timeout=20)
+    finally:
+        event_bus.unsubscribe(q)
+"""
+import asyncio
+from typing import Any
+
+_subscribers: set[asyncio.Queue] = set()
+
+
+def subscribe() -> asyncio.Queue:
+    q: asyncio.Queue = asyncio.Queue()
+    _subscribers.add(q)
+    return q
+
+
+def unsubscribe(q: asyncio.Queue) -> None:
+    _subscribers.discard(q)
+
+
+async def publish(event: dict[str, Any]) -> None:
+    for q in list(_subscribers):
+        await q.put(event)