ops: wait for the database on startup (no crash-loop on a slow DB)

New thoughtsync.dbwait polls the DB (SELECT 1) up to 60×1s before startup,
logging each attempt, so a briefly slow/unready database no longer crash-
loops the container. Wired as `python -m thoughtsync.dbwait &&` ahead of
`alembic upgrade head` in the image CMD and the dev compose command; exits
non-zero after the window so a restart policy can take over. Prod compose
gains restart: unless-stopped as the complementary piece.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

docker-compose.dev.yml

@@ -40,9 +40,10 @@ services:
       - thoughtsync-dev-data:/var/thoughtsync
     ports:
       - "5000:5000"
-    # Install deps, run migrations, then serve with live reload on the mounted src.
+    # Install deps, wait for the DB, run migrations, then serve with live reload.
     command: >
       sh -c "pip install --quiet -e . &&
+             python -m thoughtsync.dbwait &&
              alembic upgrade head &&
              hypercorn 'thoughtsync.app:create_app()' --bind 0.0.0.0:5000 --reload"