feat: add delivery sequence numbers + major server/client refactor

Delivery sequence numbers (MLS epoch ordering fix):
- schemas/node.capnp: add Envelope{seq,data} struct; enqueue returns seq:UInt64;
  fetch/fetchWait return List(Envelope) instead of List(Data)
- storage.rs: Store trait enqueue returns u64; fetch/fetch_limited return
  Vec<(u64, Vec<u8>)>; FileBackedStore gains QueueMapV3 with per-inbox seq
  counters and V2→V3 on-disk migration
- migrations/002_add_seq.sql: seq column, delivery_seq_counters table, index
- sql_store.rs: atomic UPSERT counter via RETURNING, ORDER BY seq, SCHEMA_VERSION→3
- node_service/delivery.rs: builds Envelope list; returns seq from enqueue
- client/rpc.rs: enqueue→u64, fetch_all/fetch_wait→Vec<(u64,Vec<u8>)>
- client/commands.rs: sort-by-seq before MLS processing; retry loop in cmd_recv
  and receive_pending_plaintexts for correct epoch ordering

Server refactor:
- Split monolithic main.rs into node_service/{mod,delivery,auth_ops,key_ops,p2p_ops}
- Add auth.rs (token validation, rate limiting), config.rs, metrics.rs, tls.rs
- Add SQL migrations runner (001_initial.sql, 002_add_seq.sql)
- OPAQUE PAKE login/registration, sealed-sender mode, queue depth limit (1000)

Client refactor:
- Split lib.rs into client/{commands,rpc,state,retry,hex,mod}
- Add cmd_whoami, cmd_health, cmd_check_key, cmd_ping subcommands
- Add cmd_register_user, cmd_login (OPAQUE), cmd_refresh_keypackage
- Hybrid PQ envelope (X25519 + ML-KEM-768) on all send/recv paths
- E2E test suite expanded

Other:
- quicnprotochat-gui: Tauri 2 desktop GUI skeleton (backend + HTML UI)
- quicnprotochat-p2p: iroh-based P2P transport stub
- quicnprotochat-core: app_message, hybrid_crypto modules; GroupMember API updates
- .github/workflows/size-lint.yml: binary size regression check
- docs: protocol comparison, roadmap updates, fully-operational checklist

crates/quicnprotochat-server/migrations/001_initial.sql

@@ -0,0 +1,47 @@
+CREATE TABLE IF NOT EXISTS key_packages (
+    id           INTEGER PRIMARY KEY AUTOINCREMENT,
+    identity_key BLOB NOT NULL,
+    package_data BLOB NOT NULL,
+    created_at   INTEGER DEFAULT (strftime('%s','now'))
+);
+
+CREATE TABLE IF NOT EXISTS deliveries (
+    id            INTEGER PRIMARY KEY AUTOINCREMENT,
+    recipient_key BLOB NOT NULL,
+    channel_id    BLOB NOT NULL DEFAULT X'',
+    payload       BLOB NOT NULL,
+    created_at    INTEGER DEFAULT (strftime('%s','now'))
+);
+
+CREATE TABLE IF NOT EXISTS hybrid_keys (
+    identity_key      BLOB PRIMARY KEY,
+    hybrid_public_key BLOB NOT NULL
+);
+
+CREATE INDEX IF NOT EXISTS idx_kp_identity
+    ON key_packages(identity_key);
+
+CREATE INDEX IF NOT EXISTS idx_del_recipient_channel
+    ON deliveries(recipient_key, channel_id);
+
+CREATE TABLE IF NOT EXISTS server_setup (
+    id         INTEGER PRIMARY KEY CHECK (id = 1),
+    setup_data BLOB NOT NULL
+);
+
+CREATE TABLE IF NOT EXISTS users (
+    username      TEXT PRIMARY KEY,
+    opaque_record BLOB NOT NULL,
+    created_at    INTEGER DEFAULT (strftime('%s','now'))
+);
+
+CREATE TABLE IF NOT EXISTS user_identity_keys (
+    username     TEXT PRIMARY KEY,
+    identity_key BLOB NOT NULL
+);
+
+CREATE TABLE IF NOT EXISTS endpoints (
+    identity_key BLOB PRIMARY KEY,
+    node_addr    BLOB NOT NULL,
+    updated_at   INTEGER DEFAULT (strftime('%s','now'))
+);