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>

bun.lock

@@ -43,6 +43,15 @@
         "hono": "^4.12.12",
       },
     },
+    "packages/shade-storage-sqlite": {
+      "name": "@shade/storage-sqlite",
+      "version": "0.1.0",
+      "dependencies": {
+        "@shade/core": "workspace:*",
+        "@shade/crypto-web": "workspace:*",
+        "@shade/server": "workspace:*",
+      },
+    },
     "packages/shade-transport": {
       "name": "@shade/transport",
       "version": "0.1.0",
@@ -67,6 +76,8 @@
 
     "@shade/server": ["@shade/server@workspace:packages/shade-server"],
 
+    "@shade/storage-sqlite": ["@shade/storage-sqlite@workspace:packages/shade-storage-sqlite"],
+
     "@shade/transport": ["@shade/transport@workspace:packages/shade-transport"],
 
     "@types/node": ["@types/node@25.5.2", "", { "dependencies": { "undici-types": "~7.18.0" } }, "sha512-tO4ZIRKNC+MDWV4qKVZe3Ql/woTnmHDr5JD8UI5hn2pwBrHEwOEMZK7WlNb5RKB6EoJ02gwmQS9OrjuFnZYdpg=="],