Fix TTS memory leaks causing failure after extended usage

[Copilot]

TTS stops working after prolonged app usage on iOS/Android due to AudioPlayer resource leaks and unbounded cache growth.

Core Issues

AudioPlayer resource leaks:

• Event listeners not removed in error paths
• Existing players not cleaned up before creating new ones
• play() failures leave resources dangling

Unbounded memory growth:

• TTS cache grows indefinitely (one entry per station announcement)
• No size limit causes eventual memory exhaustion

Changes

src/hooks/useTTS.ts

• Pre-cleanup existing players before instantiation
• Wrap all resource cleanup in try-catch (defensive against partial failures)
• Add error handling to play() with full resource teardown on failure
• Enhanced error logging for fetchSpeech() and HTTP failures

src/hooks/useTTSCache.ts

• Implement FIFO cache with MAX_CACHE_SIZE = 50
• Auto-evict oldest entries when limit exceeded

src/hooks/useTTSCache.test.ts

• Verify cache eviction at capacity
• Confirm FIFO ordering preserved

Example

Before:

const soundJa = createAudioPlayer({ uri: pathJa });  // Old player leaks
soundJa.play();  // Throws but leaves listeners attached

After:

// Cleanup existing
soundJaRef.current?.pause();
soundJaRef.current?.remove();

const soundJa = createAudioPlayer({ uri: pathJa });
try {
  soundJa.play();
} catch (e) {
  // Full teardown on failure
  jaRemoveListener?.remove();
  soundJa.remove();
}

Note

File system cache (MP3 files) still unbounded - follow-up issue for disk cleanup strategy.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>長時間使用しているとTTSが動作しなくなることがある</issue_title>
<issue_description>iOS/Androidどちらでも再現。functionsの処理も考慮して調査が必要。</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes 長時間使用しているとTTSが動作しなくなることがある #4614

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