Phase 7: Bot/extension system

Bot accounts (User rows with is_bot=True), scoped API tokens (read:messages,
write:messages, manage:rooms) authenticated via Authorization: Bearer on both
REST and the WS handshake, live bot WebSocket access on the same /ws/chat
endpoint humans use, message editing (WS "edit" envelope -> message_update
broadcast, fans out cross-instance for free via the existing broadcaster),
incoming webhooks (room-scoped, no auth beyond the URL token), and outgoing
webhooks/event subscriptions (HMAC-SHA256 signed, backgrounded delivery,
creation-time SSRF validation against private/loopback/link-local targets).

Token auth is additive, not a parallel system: a bearer-token-authenticated
bot goes through the exact same room-membership/role checks a session-
authenticated human does everywhere; only read:messages/write:messages are
separately scope-gated (the two message endpoints). manage:rooms scope
enforcement, full per-delivery SSRF re-validation, and bot API rate limiting
were explicitly scoped out (confirmed with the repo owner) as disproportionate
to this phase -- documented as known gaps in backend/README.md rather than
silently skipped.

Admin portal gains a Bots tab (create bots, issue/revoke scoped tokens,
cross-room webhook visibility); RoomInfoPanel gains room-scoped webhook/
subscription management, mirroring how invites already work there. The chat
UI also gets a minimal "edit your own message" affordance -- not asked for
by the issue, but the only practical way to exercise the edit pipeline by
hand instead of only via a scripted bot client.

Along the way: fixed a real bug caught while writing the incoming-webhook
test -- offline-push notification relied on the sender being "connected" to
exclude themselves, true for WS-originated messages but not for the new
webhook path, which has no WS connection for the attributed sender at all.
Now explicitly excluded. Also discovered the REST-only test fixture never
triggered ASGI lifespan, so app.state.broadcaster/presence didn't exist for
it; moved their construction out of the lifespan into create_app() itself
(Redis client construction is synchronous/lazy) so both the WS and
REST-only paths always have them.

New tests/test_bots.py, test_message_edit.py, test_webhooks.py (full suite
now 78/78, stable across repeated runs) plus a scripted end-to-end smoke
test (bot WS join/post/edit, incoming webhook, SSRF rejection, outgoing
delivery) and a full browser walkthrough of the new admin/room UI.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/app/services/webhook_delivery.py

@@ -0,0 +1,41 @@
+import hashlib
+import hmac
+import json
+import logging
+
+import httpx
+
+from app.models import EventSubscription
+
+logger = logging.getLogger(__name__)
+
+_TIMEOUT_SECONDS = 5.0
+
+
+async def deliver_event(subscription: EventSubscription, event_type: str, payload: dict) -> None:
+    """POST a signed event to a subscription's target_url.
+
+    Fire-once, best-effort: no retry/backoff, any failure is logged and
+    swallowed rather than raised -- a slow or dead third-party endpoint must
+    never affect message delivery to real room members. Safe to run in a
+    background asyncio.create_task (unlike the Phase 4 push lesson) because
+    there's no DB session involved here, just the already-serialized
+    payload and secret -- nothing that can outlive an event loop.
+    """
+    body = json.dumps({"event": event_type, "data": payload}).encode()
+    signature = hmac.new(subscription.signing_secret.encode(), body, hashlib.sha256).hexdigest()
+
+    try:
+        async with httpx.AsyncClient(timeout=_TIMEOUT_SECONDS) as client:
+            await client.post(
+                subscription.target_url,
+                content=body,
+                headers={
+                    "Content-Type": "application/json",
+                    "X-KeepItTalking-Signature": f"sha256={signature}",
+                },
+            )
+    except httpx.HTTPError:
+        logger.warning(
+            "Failed to deliver %s event to subscription %s", event_type, subscription.id
+        )