feat(journal): farm-journal maubot plugin

Records what people did each day, scoped per-room/sender/timestamp.
Stored in maubot's per-instance SQLite plugin DB.

Commands:
- !journal <text>     record an entry
- !journal show [@u]  last 10 entries, optionally filtered by user
- !journal today      everything logged today (UTC)

The command shape requires @command.new(arg_fallthrough=False) so
the parent's pass_raw=True `text` argument doesn't swallow
subcommand keywords like "show" and "today" — same pattern the
upstream maubot reminder plugin uses.

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

.gitignore

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+*.mbp
+__pycache__/
+*.pyc
+.venv/