fix(stt): graceful degradation for Expo Go

Handle missing native module @jamsch/expo-speech-recognition gracefully.
In Expo Go the native module is not available, which was causing the entire
_layout.tsx to fail to export, breaking tab navigation.

- Use dynamic require() with try/catch instead of static import
- Initialize ExpoSpeechRecognitionModule and useSpeechRecognitionEvent as no-ops
- Check module availability before calling any native methods
- isAvailable state properly reflects module presence

Tab navigation now works in Expo Go (with STT disabled).
Full STT functionality requires a development build.

hooks/useSpeechRecognition.ts

@@ -4,6 +4,10 @@
  * Wraps @jamsch/expo-speech-recognition for easy use in components.
  * Provides start/stop controls, recognized text, and status states.
  *
+ * NOTE: Gracefully handles missing native module (Expo Go)
+ * - In Expo Go: isAvailable = false, all methods are no-ops
+ * - In Dev Build: Full functionality
+ *
  * Usage:
  * ```typescript
  * const { startListening, stopListening, isListening, recognizedText, error } = useSpeechRecognition();
@@ -19,12 +23,20 @@
  */
 
 import { useState, useCallback, useRef, useEffect } from 'react';
-import {
-  ExpoSpeechRecognitionModule,
-  useSpeechRecognitionEvent,
-} from '@jamsch/expo-speech-recognition';
 import { Platform } from 'react-native';
 
+// Try to import the native module - may fail in Expo Go
+let ExpoSpeechRecognitionModule: any = null;
+let useSpeechRecognitionEvent: any = () => {}; // no-op by default
+
+try {
+  const speechRecognition = require('@jamsch/expo-speech-recognition');
+  ExpoSpeechRecognitionModule = speechRecognition.ExpoSpeechRecognitionModule;
+  useSpeechRecognitionEvent = speechRecognition.useSpeechRecognitionEvent;
+} catch (e) {
+  console.warn('[SpeechRecognition] Native module not available (Expo Go?). Speech recognition disabled.');
+}
+
 export interface UseSpeechRecognitionOptions {
   /** Language for recognition (default: 'en-US') */
   lang?: string;
@@ -83,7 +95,7 @@ export function useSpeechRecognition(
   } = options;
 
   const [isListening, setIsListening] = useState(false);
-  const [isAvailable, setIsAvailable] = useState(true);
+  const [isAvailable, setIsAvailable] = useState(!!ExpoSpeechRecognitionModule);
   const [recognizedText, setRecognizedText] = useState('');
   const [partialTranscript, setPartialTranscript] = useState('');
   const [error, setError] = useState<string | null>(null);
@@ -95,6 +107,11 @@ export function useSpeechRecognition(
 
   // Check availability on mount
   useEffect(() => {
+    if (!ExpoSpeechRecognitionModule) {
+      setIsAvailable(false);
+      return;
+    }
+
     const checkAvailability = async () => {
       try {
         // Check if we can get permissions (indirect availability check)
@@ -131,7 +148,7 @@ export function useSpeechRecognition(
   });
 
   // Event: Result available
-  useSpeechRecognitionEvent('result', (event) => {
+  useSpeechRecognitionEvent('result', (event: any) => {
     const results = event.results;
     if (results && results.length > 0) {
       const result = results[results.length - 1];
@@ -159,7 +176,7 @@ export function useSpeechRecognition(
   });
 
   // Event: Error occurred
-  useSpeechRecognitionEvent('error', (event) => {
+  useSpeechRecognitionEvent('error', (event: any) => {
     const errorMessage = event.message || event.error || 'Speech recognition error';
     console.error('[SpeechRecognition] Error:', errorMessage);
 
@@ -178,6 +195,11 @@ export function useSpeechRecognition(
    * @returns true if started successfully, false otherwise
    */
   const startListening = useCallback(async (): Promise<boolean> => {
+    if (!ExpoSpeechRecognitionModule) {
+      console.warn('[SpeechRecognition] Cannot start - native module not available');
+      return false;
+    }
+
     if (isListening || isStartingRef.current) {
       console.log('[SpeechRecognition] Already listening or starting');
       return false;
@@ -239,6 +261,8 @@ export function useSpeechRecognition(
    * Stop listening and process final result
    */
   const stopListening = useCallback(() => {
+    if (!ExpoSpeechRecognitionModule) return;
+
     if (!isListening && !isStartingRef.current) {
       console.log('[SpeechRecognition] Not listening, nothing to stop');
       return;
@@ -256,6 +280,8 @@ export function useSpeechRecognition(
    * Abort listening without processing
    */
   const abortListening = useCallback(() => {
+    if (!ExpoSpeechRecognitionModule) return;
+
     if (!isListening && !isStartingRef.current) {
       return;
     }