feat(speech): add prompt voice input (#249)

## Summary
- add server-backed speech capabilities and transcription endpoints plus
UI settings for speech configuration
- add push-to-talk prompt voice input with microphone controls,
transcription insertion, and browser capability gating
- keep prompt controls aligned by restoring right-side nav placement and
moving the mic beside the expand control

packages/ui/src/components/settings/appearance-settings-section.tsx

@@ -24,6 +24,7 @@ export const AppearanceSettingsSection: Component = () => {
     toggleUsageMetrics,
     toggleAutoCleanupBlankSessions,
     togglePromptSubmitOnEnter,
+    toggleShowPromptVoiceInput,
     setDiffViewMode,
     setToolOutputExpansion,
     setDiagnosticsExpansion,
@@ -38,10 +39,11 @@ export const AppearanceSettingsSection: Component = () => {
       toggleShowThinkingBlocks,
       toggleKeyboardShortcutHints,
       toggleShowTimelineTools,
-      toggleUsageMetrics,
-      toggleAutoCleanupBlankSessions,
-      togglePromptSubmitOnEnter,
-      setDiffViewMode,
+        toggleUsageMetrics,
+        toggleAutoCleanupBlankSessions,
+        togglePromptSubmitOnEnter,
+        toggleShowPromptVoiceInput,
+        setDiffViewMode,
       setToolOutputExpansion,
       setDiagnosticsExpansion,
       setThinkingBlocksExpansion,