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>

journal/maubot.yaml

@@ -0,0 +1,9 @@
+maubot: 0.1.0
+id: dev.aiolabs.journal
+version: 0.1.3
+license: AGPL-3.0-or-later
+modules:
+  - journal
+main_class: JournalBot
+database: true
+database_type: asyncpg