Signal chats in the app (desktop only) with a chat button on every screen

- signal.js: talks to signal-cli-rest-api (a linked device of your Signal account); keeps conversations in /data/signal; live updates; send/receive text, files, replies, reactions, groups, receipts
- Signal tab and a floating chat panel on every screen, shown only on desktop-class windows; new Signal permission per person
- compose: signal bridge container sharing the hub's network
- tools/signal-test.js (fake bridge), README

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

.gitea/workflows/build.yml

@@ -21,6 +21,7 @@ jobs:
       - run: node tools/users-test.js   # accounts: private data, tab limits, invites, migration
       - run: node tools/plex-test.js    # Plex sign-in stays signed in and repairs itself
       - run: node tools/player-test.js  # music player: queue, shuffle/repeat, stall recovery
+      - run: node tools/signal-test.js  # Signal: linking, messages, sending, live updates
       - run: node tools/webmail-test.js # the /webmail/ pass-through to the bundled webmail (Cypht)
 
       - uses: docker/setup-buildx-action@v3