feat: implement account recovery with encrypted backup bundles

Add recovery code generation (8 codes per setup), Argon2id key derivation,
ChaCha20-Poly1305 encrypted bundles, and server-side zero-knowledge storage.
Each code independently recovers the account. Includes core crypto module,
protobuf service (method IDs 750-752), server domain + handlers, SDK methods,
SQL migration, and CLI commands (/recovery setup, /recovery restore).

proto/qpq/v1/recovery.proto

@@ -0,0 +1,37 @@
+syntax = "proto3";
+package qpq.v1;
+
+// Recovery service — encrypted recovery bundle storage.
+// Method IDs: 750-752.
+
+message StoreRecoveryBundleRequest {
+  // SHA-256(recovery_token) — server-side lookup key.
+  bytes token_hash = 1;
+  // Encrypted recovery bundle (opaque to server).
+  bytes bundle = 2;
+  // TTL in seconds (default 90 days = 7776000).
+  uint64 ttl_secs = 3;
+}
+
+message StoreRecoveryBundleResponse {
+  bool success = 1;
+}
+
+message FetchRecoveryBundleRequest {
+  // SHA-256(recovery_token) — lookup key.
+  bytes token_hash = 1;
+}
+
+message FetchRecoveryBundleResponse {
+  // Empty if no bundle found.
+  bytes bundle = 1;
+}
+
+message DeleteRecoveryBundleRequest {
+  // SHA-256(recovery_token) — lookup key.
+  bytes token_hash = 1;
+}
+
+message DeleteRecoveryBundleResponse {
+  bool success = 1;
+}