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>

cmd/daemon/main.go

@@ -7,12 +7,14 @@ import (
 	"flag"
 	"log"
 	"os"
+	"path/filepath"
 
 	"github.com/waste-go/internal/anchor"
 	"github.com/waste-go/internal/crypto"
 	"github.com/waste-go/internal/ipc"
 	"github.com/waste-go/internal/mesh"
 	"github.com/waste-go/internal/proto"
+	"github.com/waste-go/internal/store"
 )
 
 func main() {
@@ -22,13 +24,20 @@ func main() {
 	anchorURL := flag.String("anchor", "", "anchor WebSocket URL, e.g. ws://your-vps:17339/ws")
 	flag.Parse()
 
-	id, err := crypto.LoadOrCreate(expandHome(*dataDir), *alias)
+	dir := expandHome(*dataDir)
+	id, err := crypto.LoadOrCreate(dir, *alias)
 	if err != nil {
 		log.Fatalf("identity: %v", err)
 	}
 	log.Printf("daemon: local peer id: %s  alias: %s", id.PeerID().Short(), id.Alias)
 
-	m := mesh.New(id)
+	st, err := store.Open(filepath.Join(dir, "messages.db"))
+	if err != nil {
+		log.Fatalf("store: %v", err)
+	}
+	defer st.Close()
+
+	m := mesh.New(id, st)
 
 	// joinFn is passed to the IPC layer; it's called when the UI sends join_network.
 	joinFn := func(ctx context.Context, networkName string) {