feat(web): service-worker notifications and composer/scroll UX fixes

- register notifications service worker and handle click-to-open chat/message

- route realtime notifications through service worker with fallback

- support ?chat=&message= deep-link navigation in chats page

- enforce 1s minimum voice message length

- lift scroll-to-bottom button to avoid overlap with composer action

web/src/components/MessageComposer.tsx

@@ -280,15 +280,21 @@ export function MessageComposer() {
       recorder.ondataavailable = (event) => chunksRef.current.push(event.data);
       recorder.onstop = async () => {
         const shouldSend = sendVoiceOnStopRef.current;
+        const durationMs = recordingStartedAtRef.current ? Date.now() - recordingStartedAtRef.current : 0;
         const data = [...chunksRef.current];
         chunksRef.current = [];
         if (recordingStreamRef.current) {
           recordingStreamRef.current.getTracks().forEach((track) => track.stop());
           recordingStreamRef.current = null;
         }
+        recordingStartedAtRef.current = null;
         if (!shouldSend || data.length === 0) {
           return;
         }
+        if (durationMs < 1000) {
+          setUploadError("Voice message is too short. Minimum length is 1 second.");
+          return;
+        }
         const blob = new Blob(data, { type: "audio/webm" });
         const file = new File([blob], `voice-${Date.now()}.webm`, { type: "audio/webm" });
         await handleUpload(file, "voice");
@@ -313,7 +319,6 @@ export function MessageComposer() {
       recorderRef.current.stop();
     }
     recorderRef.current = null;
-    recordingStartedAtRef.current = null;
     setRecordingState("idle");
     setRecordSeconds(0);
   }
@@ -567,8 +572,9 @@ export function MessageComposer() {
             disabled={recordingState !== "idle" || !activeChatId}
             onClick={handleSend}
             type="button"
+            title="Send message"
           >
-            ➤
+            ↑
           </button>
         ) : (
           <button
@@ -578,6 +584,7 @@ export function MessageComposer() {
             disabled={isUploading || !activeChatId}
             onPointerDown={onMicPointerDown}
             type="button"
+            title="Hold to record voice"
           >
             🎤
           </button>

web/src/components/MessageList.tsx

@@ -494,11 +494,12 @@ export function MessageList() {
 
       <div className="px-5 pb-2 text-xs text-slate-300/80">{(typingByChat[activeChatId] ?? []).length > 0 ? "typing..." : ""}</div>
       {showScrollToBottom ? (
-        <div className="pointer-events-none absolute bottom-4 right-4 z-40">
+        <div className="pointer-events-none absolute bottom-20 right-4 z-40 md:bottom-24">
           <button
             className="pointer-events-auto inline-flex h-10 w-10 items-center justify-center rounded-full border border-slate-600/80 bg-slate-900/90 text-lg text-slate-100 shadow-lg hover:bg-slate-800"
             onClick={scrollToBottom}
             type="button"
+            title="Scroll to latest"
           >
             ↓
           </button>