feat(gmail): take the star off a mail once it has become a task

A starred Gmail message became a task and kept its star, so a starred inbox only
grew — the IMAP side has always unflagged what it imports, and Gmail could not,
because the scope was gmail.readonly. This gives Gmail the same one write: after
the task is made, the STARRED label comes off the message, in one batchModify for
the whole sweep. Nothing else is touched — not the body, not other labels, and a
label trigger's label stays where it is, since that label is the person's own.

The scope goes from gmail.readonly to gmail.modify, which is the narrowest scope
Google offers that can remove a label. An existing connection keeps working on its
old read-only grant — the sync still reads, the unstar is a best-effort 403 that is
logged, not fatal — and starts clearing stars once the account is reconnected and
the new grant is in place. It self-heals: a mail that could not be unstarred stays
starred, stays in the next query, and is tried again.

The consent screen now asks for more than it used to; the settings copy, the docs
and the scope table all say modify rather than read-only in the same change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -103,7 +103,7 @@ Apple Reminders, forward mail into it, and add it to Claude as a connector.
 | CalDAV server (two-way VTODO) | Done, tested |
 | Mail-to-task | Done, tested |
 | AI layer (Anthropic/OpenAI/Google/local) | Built, degrades when unconfigured |
-| Gmail: OAuth2 with PKCE, polling, one-way to tasks | Done, tested |
+| Gmail: OAuth2 with PKCE, polling to tasks, unstars what it imports | Done, tested |
 | Google Calendar: read-only, laid over the task calendar | Built, never run against Google |
 | Calendar subscriptions: ICS and webcal, several per person | Done, tested |
 | Times on tasks, set by dragging in the week grid | Done, tested |