ipc: promote startup socket-wait to a shared DialWait; use in all modules

The cold-start crash-loop wasn't mavweb-specific — mavpoll and mavcaldav also
ipc.Dial + exit on failure, so they crash-looped until core booted too. Moved
the retry into ipc.DialWait (capped backoff, bounded) and switched mavweb,
mavpoll, mavcaldav to it. mavweb's local dialCoreWithRetry is gone.

Test: server appears after DialWait starts → it waits and connects.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/ipc/ipc_test.go

@@ -57,6 +57,46 @@ func newServerWithStore(t *testing.T) (CoreAPI, *Server, *Client, *store.Store)
 	return api, srv, cli, s
 }
 
+// TestDialWait_WaitsForLateServer — a module may start before core's socket
+// exists (core loads models first). DialWait must keep retrying until the
+// socket appears rather than fail on the first attempt.
+func TestDialWait_WaitsForLateServer(t *testing.T) {
+	dir := t.TempDir()
+	sock := filepath.Join(dir, "maven.sock")
+	srvCh := make(chan *Server, 1)
+	errCh := make(chan error, 1)
+
+	// bring the server up only after DialWait is already retrying
+	go func() {
+		time.Sleep(300 * time.Millisecond)
+		s, err := store.Open(context.Background(), filepath.Join(dir, "maven.db"))
+		if err != nil {
+			errCh <- err
+			return
+		}
+		t.Cleanup(func() { _ = s.Close() })
+		srv, err := Listen(sock, NewStoreAPI(s))
+		if err != nil {
+			errCh <- err
+			return
+		}
+		go func() { _ = srv.Serve() }()
+		srvCh <- srv
+	}()
+
+	cli, err := DialWait(sock, 5*time.Second)
+	if err != nil {
+		t.Fatalf("DialWait should connect once the server appears: %v", err)
+	}
+	select {
+	case err := <-errCh:
+		t.Fatalf("server setup failed: %v", err)
+	case srv := <-srvCh:
+		_ = cli.Close() // close client first so srv.Close's handler wait returns
+		_ = srv.Close()
+	}
+}
+
 // TestClient_ReconnectsAfterServerRestart — a long-lived module (e.g. mavweb)
 // must survive a core restart. The first server is closed and a new one is
 // brought up on the SAME socket path (as a daemon restart does); the client's