Improve SQLite concurrency and fix AV1 transcoding false positives

[Copilot]

SQLite lock contention under concurrent requests, plus valid AV1 files incorrectly flagged as corrupt during transcoding.

SQLite Performance

• Use NullPool - Connection pooling doesn't benefit file-based SQLite and causes stale connection issues
• Add timeout=30 to connection args for lock wait tolerance
• Set check_same_thread=False for multi-threaded Flask access (safe with existing WAL mode)
• Applied same config to APScheduler's SQLAlchemyJobStore

app.config['SQLALCHEMY_ENGINE_OPTIONS'] = {
    'poolclass': NullPool,
    'connect_args': {
        'timeout': 30,
        'check_same_thread': False,
    },
}

AV1 Transcoding

• Added "invalid data found when processing input" to AV1_FALSE_POSITIVE_INDICATORS
• This ffmpeg warning occurs with valid AV1 files but wasn't being ignored like other known AV1 false positives

Original prompt

Is there anything that can be done to improve sqlite's performance. It seems like right now that it gets locked up if there are too many requests.

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