feat: Migrate voice capture to composable with floating push-to-talk

Extract voice recording logic from FloatingVoice.vue into useVoiceCapture
composable. TranscriptCard now does real recording instead of mock typing.
InputSettings allows voice mode toggle (WebSpeech/Whisper GPU), mic
selection, and debug audio playback. ChatInput gets a settings gear button.

Long-press on FloatBubble shows a floating TranscriptCard (push-to-talk)
instead of opening the full PromptBar. Release stops recording after a
500ms buffer. Click still opens PromptBar normally.

Parallel MediaRecorder captures raw audio in WebSpeech mode for DB save
and debug playback. Transient errors (no-speech) no longer kill sessions.
Touch selection prevention on FloatBubble for tablets.

frontend/src/components/agent/FloatBubble.vue

@@ -11,9 +11,10 @@ const props = defineProps<{
 const emit = defineEmits<{
   click: [event: MouseEvent]
   hold: [el: HTMLElement]
+  holdrelease: []
 }>()
 
-const HOLD_MS = 400
+const HOLD_MS = 200
 let holdTimer: number | null = null
 let didHold = false
 let holdTarget: HTMLElement | null = null
@@ -30,13 +31,18 @@ function onPointerDown(e: PointerEvent) {
 
 function onPointerUp(e: PointerEvent) {
   clearHold()
-  if (!didHold) {
+  if (didHold) {
+    emit('holdrelease')
+  } else {
     emit('click', e as unknown as MouseEvent)
   }
 }
 
 function onPointerCancel() {
   clearHold()
+  if (didHold) {
+    emit('holdrelease')
+  }
 }
 
 function clearHold() {
@@ -124,7 +130,10 @@ function bubbleTitle() {
     @pointerdown.prevent="onPointerDown"
     @pointerup="onPointerUp"
     @pointercancel="onPointerCancel"
+    @touchstart.prevent
     @contextmenu.prevent
+    @selectstart.prevent
+    @dragstart.prevent
     @mouseenter="!isAnimating() && (($event.currentTarget as HTMLElement).style.boxShadow = bubbleHoverShadow())"
     @mouseleave="!isAnimating() && (($event.currentTarget as HTMLElement).style.boxShadow = bubbleStyle().boxShadow || '')"
   >
@@ -194,7 +203,8 @@ function bubbleTitle() {
   -webkit-user-select: none;
   user-select: none;
   -webkit-touch-callout: none;
-  touch-action: manipulation;
+  -webkit-tap-highlight-color: transparent;
+  touch-action: none;
   position: relative;
 }
 
@@ -543,6 +553,14 @@ function bubbleTitle() {
   50% { opacity: 0.7; }
 }
 
+/* Prevent touch selection on all children */
+.agent-bubble * {
+  -webkit-user-select: none;
+  user-select: none;
+  -webkit-touch-callout: none;
+  pointer-events: none;
+}
+
 /* ====================== LABELS ====================== */
 
 .bubble-label {