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_test.go

@@ -0,0 +1,103 @@
+package store
+
+import (
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/waste-go/internal/proto"
+)
+
+func TestRoundTrip(t *testing.T) {
+	st, err := Open(filepath.Join(t.TempDir(), "test.db"))
+	if err != nil {
+		t.Fatalf("Open: %v", err)
+	}
+	defer st.Close()
+
+	msg := &proto.ChatMessage{
+		Mid:    "aabbccdd00112233",
+		From:   proto.PeerID("deadbeef"),
+		Room:   "general",
+		Body:   "hello world",
+		SentAt: time.Now().UTC().Truncate(time.Second),
+	}
+
+	if err := st.SaveMessage(msg); err != nil {
+		t.Fatalf("SaveMessage: %v", err)
+	}
+
+	// Duplicate mid must be silently ignored.
+	if err := st.SaveMessage(msg); err != nil {
+		t.Fatalf("duplicate SaveMessage: %v", err)
+	}
+
+	msgs, err := st.RecentMessages("general", 10)
+	if err != nil {
+		t.Fatalf("RecentMessages: %v", err)
+	}
+	if len(msgs) != 1 {
+		t.Fatalf("got %d messages, want 1", len(msgs))
+	}
+	got := msgs[0]
+	if got.Mid != msg.Mid || got.Body != msg.Body || got.Room != msg.Room {
+		t.Fatalf("message mismatch: %+v", got)
+	}
+}
+
+func TestSavePeerAndKnownPeers(t *testing.T) {
+	st, err := Open(filepath.Join(t.TempDir(), "test.db"))
+	if err != nil {
+		t.Fatalf("Open: %v", err)
+	}
+	defer st.Close()
+
+	if err := st.SavePeer("aabbccdd", "alice"); err != nil {
+		t.Fatalf("SavePeer: %v", err)
+	}
+	// Upsert with updated alias.
+	if err := st.SavePeer("aabbccdd", "alice-updated"); err != nil {
+		t.Fatalf("SavePeer upsert: %v", err)
+	}
+
+	peers, err := st.KnownPeers()
+	if err != nil {
+		t.Fatalf("KnownPeers: %v", err)
+	}
+	if peers["aabbccdd"] != "alice-updated" {
+		t.Fatalf("alias = %q, want %q", peers["aabbccdd"], "alice-updated")
+	}
+}
+
+func TestRecentMessagesOrdering(t *testing.T) {
+	st, err := Open(filepath.Join(t.TempDir(), "test.db"))
+	if err != nil {
+		t.Fatalf("Open: %v", err)
+	}
+	defer st.Close()
+
+	base := time.Now().UTC().Truncate(time.Second)
+	for i := range 5 {
+		st.SaveMessage(&proto.ChatMessage{
+			Mid:    string(rune('a'+i)) + "000000000000000",
+			From:   "deadbeef",
+			Room:   "general",
+			Body:   string(rune('a' + i)),
+			SentAt: base.Add(time.Duration(i) * time.Second),
+		})
+	}
+
+	msgs, err := st.RecentMessages("general", 10)
+	if err != nil {
+		t.Fatalf("RecentMessages: %v", err)
+	}
+	if len(msgs) != 5 {
+		t.Fatalf("got %d messages, want 5", len(msgs))
+	}
+	// Must be oldest-first.
+	for i := 1; i < len(msgs); i++ {
+		if msgs[i].SentAt.Before(msgs[i-1].SentAt) {
+			t.Fatalf("messages not in ascending order at index %d", i)
+		}
+	}
+}