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>

cmd/mavcaldav/main.go

@@ -58,7 +58,7 @@ func run(args []string) error {
 	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
 	defer stop()
 
-	core, err := ipc.Dial(*socket)
+	core, err := ipc.DialWait(*socket, 60*time.Second)
 	if err != nil {
 		return err
 	}

cmd/mavpoll/main.go

@@ -69,7 +69,7 @@ func run(args []string) error {
 	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
 	defer stop()
 
-	core, err := ipc.Dial(*socket)
+	core, err := ipc.DialWait(*socket, 60*time.Second)
 	if err != nil {
 		return err
 	}

cmd/mavweb/main.go

@@ -87,7 +87,7 @@ func main() {
 
 	var core ipc.CoreAPI
 	if *coreSock != "" {
-		c, err := dialCoreWithRetry(*coreSock, 60*time.Second)
+		c, err := ipc.DialWait(*coreSock, 60*time.Second)
 		if err != nil {
 			log.Fatalf("dial core %s: %v", *coreSock, err)
 		}
@@ -169,36 +169,6 @@ func main() {
 	}
 }
 
-// dialCoreWithRetry waits for core's IPC socket to appear before giving up.
-// Core loads models on boot and (esp. under compose) may come up after mavweb;
-// depends_on only orders container start, not socket readiness. Retrying with
-// capped backoff up to timeout stops mavweb crash-looping on a cold start. A
-// core still absent past the deadline is genuinely fatal. Mid-life core
-// restarts are handled separately by ipc.Client's redial-on-drop.
-func dialCoreWithRetry(path string, timeout time.Duration) (*ipc.Client, error) {
-	deadline := time.Now().Add(timeout)
-	delay := 200 * time.Millisecond
-	for attempt := 1; ; attempt++ {
-		c, err := ipc.Dial(path)
-		if err == nil {
-			if attempt > 1 {
-				log.Printf("core socket %s ready after %d attempts", path, attempt)
-			}
-			return c, nil
-		}
-		if time.Now().After(deadline) {
-			return nil, err
-		}
-		if attempt == 1 {
-			log.Printf("waiting for core socket %s ...", path)
-		}
-		time.Sleep(delay)
-		if delay < 2*time.Second {
-			delay *= 2
-		}
-	}
-}
-
 func handleWS(w http.ResponseWriter, r *http.Request, voiceAddr string) {
 	conn, err := websocket.Accept(w, r, &websocket.AcceptOptions{
 		OriginPatterns: []string{"*"},