Add SQLite message and peer persistence (internal/store)

Each daemon writes to <data-dir>/messages.db on startup. Messages received
or sent are stored immediately; duplicate mids (INSERT OR IGNORE) are safe
to call multiple times. Peer aliases are upserted on peer_connected and
again after hello verification when the real nick is known.

Schema
- messages(mid UNIQUE, room, from_peer, body, sent_at) — mid is the YAW/2
  dedup key added in the proto migration; index on (room, sent_at) for
  efficient per-room queries.
- peers(peer_id PK, alias, last_seen) — cache of every peer ever seen,
  used to resolve hex ids to names when peers are offline.

Wiring
- store.Open called in cmd/daemon/main.go, passed to mesh.New.
- mesh.Mesh holds *store.Store (nil-safe; persistence is optional).
- mesh.SaveMessage called in dispatchPeerMessage (incoming) and ipc
  CmdSendMessage (outgoing) so the local node's own messages are stored.
- mesh.UpdatePeerAlias called after hello verification updates the alias
  with the verified nick rather than the placeholder short-id.

Messages only accumulate from join time forward — no history replay to
late-joining peers; each node's view starts from when it connected.

test-network.sh: added SQLite verification block that queries each node's
DB after the test and prints message + peer counts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/store/store.go

@@ -0,0 +1,130 @@
+// Package store persists messages and peer info to a local SQLite database.
+// Each daemon has its own database; nothing is shared across the network.
+package store
+
+import (
+	"database/sql"
+	"fmt"
+	"time"
+
+	_ "modernc.org/sqlite"
+
+	"github.com/waste-go/internal/proto"
+)
+
+const schema = `
+CREATE TABLE IF NOT EXISTS messages (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    mid         TEXT    NOT NULL UNIQUE,
+    room        TEXT    NOT NULL,
+    from_peer   TEXT    NOT NULL,
+    body        TEXT    NOT NULL,
+    sent_at     DATETIME NOT NULL
+);
+CREATE INDEX IF NOT EXISTS idx_messages_room ON messages (room, sent_at);
+
+CREATE TABLE IF NOT EXISTS peers (
+    peer_id     TEXT PRIMARY KEY,
+    alias       TEXT NOT NULL,
+    last_seen   DATETIME NOT NULL
+);
+`
+
+// Store is a local SQLite-backed message and peer store.
+type Store struct {
+	db *sql.DB
+}
+
+// Open opens (or creates) the SQLite database at path and runs migrations.
+func Open(path string) (*Store, error) {
+	db, err := sql.Open("sqlite", path)
+	if err != nil {
+		return nil, fmt.Errorf("open db: %w", err)
+	}
+	db.SetMaxOpenConns(1) // SQLite is single-writer
+	if _, err := db.Exec(schema); err != nil {
+		db.Close()
+		return nil, fmt.Errorf("migrate db: %w", err)
+	}
+	return &Store{db: db}, nil
+}
+
+// Close releases the database connection.
+func (s *Store) Close() error {
+	return s.db.Close()
+}
+
+// SaveMessage persists a chat message. Duplicate mids are silently ignored
+// (INSERT OR IGNORE), so calling this more than once is safe.
+func (s *Store) SaveMessage(msg *proto.ChatMessage) error {
+	_, err := s.db.Exec(
+		`INSERT OR IGNORE INTO messages (mid, room, from_peer, body, sent_at)
+		 VALUES (?, ?, ?, ?, ?)`,
+		msg.Mid, msg.Room, string(msg.From), msg.Body, msg.SentAt.UTC(),
+	)
+	return err
+}
+
+// SavePeer upserts a peer's alias and last-seen timestamp.
+func (s *Store) SavePeer(peerID proto.PeerID, alias string) error {
+	_, err := s.db.Exec(
+		`INSERT INTO peers (peer_id, alias, last_seen)
+		 VALUES (?, ?, ?)
+		 ON CONFLICT(peer_id) DO UPDATE SET alias=excluded.alias, last_seen=excluded.last_seen`,
+		string(peerID), alias, time.Now().UTC(),
+	)
+	return err
+}
+
+// RecentMessages returns up to limit messages for a room, oldest first.
+func (s *Store) RecentMessages(room string, limit int) ([]proto.ChatMessage, error) {
+	rows, err := s.db.Query(
+		`SELECT mid, from_peer, body, sent_at
+		 FROM messages
+		 WHERE room = ?
+		 ORDER BY sent_at DESC
+		 LIMIT ?`,
+		room, limit,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var msgs []proto.ChatMessage
+	for rows.Next() {
+		var m proto.ChatMessage
+		var from string
+		var sentAt time.Time
+		if err := rows.Scan(&m.Mid, &from, &m.Body, &sentAt); err != nil {
+			return nil, err
+		}
+		m.From = proto.PeerID(from)
+		m.Room = room
+		m.SentAt = sentAt
+		msgs = append(msgs, m)
+	}
+	// Reverse so oldest-first.
+	for i, j := 0, len(msgs)-1; i < j; i, j = i+1, j-1 {
+		msgs[i], msgs[j] = msgs[j], msgs[i]
+	}
+	return msgs, rows.Err()
+}
+
+// KnownPeers returns all peers seen since this daemon started storing data.
+func (s *Store) KnownPeers() (map[proto.PeerID]string, error) {
+	rows, err := s.db.Query(`SELECT peer_id, alias FROM peers`)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := make(map[proto.PeerID]string)
+	for rows.Next() {
+		var id, alias string
+		if err := rows.Scan(&id, &alias); err != nil {
+			return nil, err
+		}
+		out[proto.PeerID(id)] = alias
+	}
+	return out, rows.Err()
+}