docs(talk): address PR #741 reviewer nits

Comment-only follow-up to surface non-obvious behavior at the call
sites flagged in review:

- server/talk.py: note the `uuid.uuid4().hex` 32-char no-dashes format
  (spreed accepts either form).
- models/talk.py: warn that spreed returns `lastReadMessage: 0` rather
  than `null` for unread rooms, so consumers should compare to ``None``
  rather than rely on truthiness.
- 10-install-spreed-app.sh: document that the `app:install || app:enable`
  fallback also masks unrelated install failures, and limit its use to
  dev fixtures.

No runtime behavior changes; tests unchanged (still 13 unit + 7 integ).

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

nextcloud_mcp_server/models/talk.py

@@ -58,6 +58,9 @@ class TalkConversation(BaseModel):
     unreadMessages: int = 0
     unreadMention: bool = False
     lastActivity: int | None = None
+    # spreed returns `0` (not `null`) when the user has not read any
+    # message in the room yet — compare to ``None`` explicitly rather
+    # than relying on truthiness, since `0` is falsy but valid.
     lastReadMessage: int | None = None
     lastMessage: TalkMessage | None = None
     readOnly: int | None = None