synthesize() and get_stats() parsed the stored tts_speed with a bare
float(settings.get("tts_speed", "1")). The manage_settings agent tool maps
"speech speed"/"voice speed" to tts_speed and, because the setting's default is
a string, writes the value through unvalidated — so an agent (or a hand-edited
settings.json) can store "fast" or "". After that, GET /api/tts/stats and POST
/api/tts/synthesize both 500 with ValueError until the JSON is corrected by hand.
Parse defensively via a _safe_speed() helper (non-numeric/empty/<=0 -> 1.0),
mirroring the settings layer's tolerance of corrupt config.
Adds tests/test_tts_speed_malformed.py (stats + synthesize) — both raise
ValueError before this change and pass after.
TTSService._put_cache writes .mp3 for MP3 audio (ID3/MPEG-framed bytes) and
.wav otherwise, and the rest of the class treats both as cache entries
(_get_cache iterates (".mp3", ".wav"); eviction globs "*.*"). But
get_stats() enumerated the cache with `glob("*.wav")` only, so both
cache_entries and cache_size_mb undercounted — reporting 0 whenever the
cache held MP3 files, which is the common case for most TTS providers.
Glob both extensions so the reported stats match what's actually cached.
tests/test_tts_cache_stats.py writes an MP3-headed blob via _put_cache and
asserts get_stats() reports one entry with non-zero size. Fails before this
change.
