sync: overhaul sync system — device pairing, server_sequence, auto-sync, dashboards

BREAKING: replace legacy API keys with device tokens via pairing flow.
- Server: /api/client/pair, revoke, me endpoints; server_sequence + tombstones + idempotency
- Desktop client: PairDevice, GetMe, RevokeCurrent; auto-sync loop every 60s
- Config: device_token stored in separate file (0600), not config.yml
- Client DB: last_pull_seq migration for incremental pull
- Frontend (Svelte): settings modal with connect/disconnect/interval
- User dashboard (/dashboard): device list with status, revoke with password
- Admin dashboard (/admin/dashboard): devices table from /admin/api/devices
- CLI (cmd/verstak): updated for ServerSequence/GetState changes
- Fix: autoSyncLoop falls back to SQLite sync_state for server URL
- Fix: SyncSetInterval preserves server_url/device_id from SQLite

internal/core/storage/migrations_011.sql.go

@@ -0,0 +1,6 @@
+package storage
+
+// migration011 — add last_pull_seq to sync_state.
+const migration011 = `
+ALTER TABLE sync_state ADD COLUMN last_pull_seq INTEGER NOT NULL DEFAULT 0;
+`

internal/core/storage/storage.go

@@ -57,16 +57,17 @@ CREATE TABLE IF NOT EXISTS _schema_ver (
 `
 
 var migrationFiles = map[int]string{
-	1: migration001,
-	2: migration002,
-	3: migration003,
-	4: migration004,
-	5: migration005,
-	6: migration006,
+	1:  migration001,
+	2:  migration002,
+	3:  migration003,
+	4:  migration004,
+	5:  migration005,
+	6:  migration006,
 	// 7: migration007 (FTS5) — created lazily by search.Rebuild()
-	8: migration008,
-	9: migration009,
+	8:  migration008,
+	9:  migration009,
 	10: migration010,
+	11: migration011,
 }
 
 func (db *DB) runInitialSchema() error {