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>

solitaire_server/migrations/001_initial.sql

@@ -0,0 +1,32 @@
+-- Migration 001: initial schema
+-- Creates the core tables required by the Solitaire Quest sync server.
+
+CREATE TABLE IF NOT EXISTS users (
+    id                  TEXT PRIMARY KEY,           -- UUID v4
+    username            TEXT UNIQUE NOT NULL,
+    password_hash       TEXT NOT NULL,              -- bcrypt, cost 12
+    created_at          TEXT NOT NULL,              -- ISO 8601
+    leaderboard_opt_in  INTEGER NOT NULL DEFAULT 0
+);
+
+CREATE TABLE IF NOT EXISTS sync_state (
+    user_id             TEXT PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
+    stats_json          TEXT NOT NULL,
+    achievements_json   TEXT NOT NULL,
+    progress_json       TEXT NOT NULL,
+    last_modified       TEXT NOT NULL               -- ISO 8601
+);
+
+CREATE TABLE IF NOT EXISTS daily_challenges (
+    date                TEXT PRIMARY KEY,           -- "YYYY-MM-DD"
+    seed                INTEGER NOT NULL,
+    goal_json           TEXT NOT NULL
+);
+
+CREATE TABLE IF NOT EXISTS leaderboard (
+    user_id             TEXT PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
+    display_name        TEXT NOT NULL,
+    best_time_secs      INTEGER,
+    best_score          INTEGER,
+    recorded_at         TEXT NOT NULL               -- ISO 8601
+);