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/server/talk.py

@@ -188,6 +188,7 @@ def configure_talk_tools(mcp: FastMCP) -> None:
             token,
             message,
             reply_to=reply_to,
+            # 32 hex chars, no dashes — spreed accepts either UUID format.
             reference_id=uuid.uuid4().hex,
             silent=silent,
         )