feat(workspace): full server + sync implementation, all tests green

- solitaire_server: Axum auth, sync push/pull, leaderboard, daily
  challenge, account deletion, JWT middleware, rate limiting via
  tower_governor, SQLite migrations, health endpoint
- solitaire_server: expose build_test_router (no rate limiting) so
  integration tests work without a peer IP in oneshot requests
- solitaire_sync: SyncPayload, merge logic, shared API types
- solitaire_data: SyncProvider trait, LocalOnlyProvider,
  SolitaireServerClient, auth_tokens keyring integration, blanket
  Box<dyn SyncProvider> impl
- solitaire_data/settings: derive Default on SyncBackend (clippy fix)
- .sqlx/: offline query cache so server compiles without a live DB
- sqlx: removed non-existent "offline" feature flag
- keyring v2: fixed Entry::new() returning Result<Entry>
- sqlx 0.8: all SQLite TEXT columns wrapped in Option<T>
- Integration tests: max_connections(1) on in-memory pool so all
  connections share the same schema

All 191 tests pass; cargo clippy -D warnings clean.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README_SERVER.md

@@ -0,0 +1,44 @@
+# Solitaire Quest — Self-Hosting Guide
+
+## Prerequisites
+
+- Docker and Docker Compose
+- `openssl` for generating a JWT secret
+
+## Quick start
+
+1. Clone the repo and enter it.
+2. Copy the example environment file and fill in your values:
+   ```bash
+   cp .env.example .env
+   # Edit .env: set JWT_SECRET and SOLITAIRE_DOMAIN
+   ```
+3. (First time only) Generate the sqlx query cache so the server builds without a live database:
+   ```bash
+   cargo install sqlx-cli --no-default-features --features rustls,sqlite
+   export DATABASE_URL=sqlite://solitaire.db
+   sqlx database create
+   sqlx migrate run --source solitaire_server/migrations
+   cargo sqlx prepare --workspace
+   rm solitaire.db   # the real DB lives in ./data/ at runtime
+   ```
+4. Start everything:
+   ```bash
+   docker compose up -d
+   ```
+5. The server is now reachable at `https://<SOLITAIRE_DOMAIN>`.
+
+## Backups
+
+The entire server state is one SQLite file at `./data/solitaire.db`. Back it up with:
+```bash
+sqlite3 ./data/solitaire.db ".backup backup_$(date +%Y%m%d).db"
+```
+
+## Updating
+
+```bash
+git pull
+docker compose build
+docker compose up -d
+```