feat: persistent storage — SQLite backends for crash resilience

Shade sessions and keys now survive server crashes, container restarts,
and power outages via SQLite with WAL mode.

New packages:
- @shade/storage-sqlite: SQLiteStorage (StorageProvider) + SqlitePrekeyStore
  (PrekeyStore), both using bun:sqlite with auto-created tables and WAL mode
- Serialization layer in shade-core for SessionState/keys ↔ JSON/base64

Docker usage: mount volume at /data, set SHADE_DB_PATH=/data/shade-client.db
Prekey server auto-detects SHADE_PREKEY_DB_PATH for SQLite persistence

Includes crash recovery integration test: encrypt → close DB → reopen →
conversation continues seamlessly.

129 tests, 0 failures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/shade-server/src/standalone.ts

@@ -1,10 +1,22 @@
-import { createPrekeyServer } from './index.js';
+import { createPrekeyRoutes } from './routes.js';
+import type { PrekeyStore } from './store.js';
 
-const server = createPrekeyServer();
+async function createStore(): Promise<PrekeyStore> {
+  const dbPath = process.env.SHADE_PREKEY_DB_PATH;
+  if (dbPath) {
+    const { SqlitePrekeyStore } = await import('@shade/storage-sqlite');
+    console.log(`[Shade] Using SQLite prekey store: ${dbPath}`);
+    return new SqlitePrekeyStore(dbPath);
+  }
+  const { MemoryPrekeyStore } = await import('./memory-store.js');
+  console.log('[Shade] Using in-memory prekey store (data will not persist)');
+  return new MemoryPrekeyStore();
+}
 
-export default {
-  port: Number(process.env.PORT ?? 3900),
-  fetch: server.fetch,
-};
+const store = await createStore();
+const server = createPrekeyRoutes(store);
+const port = Number(process.env.PORT ?? 3900);
 
-console.log(`Shade Prekey Server listening on port ${process.env.PORT ?? 3900}`);
+export default { port, fetch: server.fetch };
+
+console.log(`Shade Prekey Server listening on port ${port}`);