⚡ Bolt: [performance improvement]

[juntaochi]

💡 What: Refactored draw_metadata and draw_progress in src/ui/mod.rs to accept an Option<&MetadataCache> parameter. Both functions now utilize Cow to borrow strings (name, artist, album, duration_str, gauge_label) directly from the cache when it's populated during the App::update tick, falling back to owned formatted strings only when the cache is unavailable.

🎯 Why: In Ratatui applications, the draw loop runs frequently (often locked to the terminal's refresh rate or input polling). Using format! macros or methods like .to_uppercase() inside the render loop causes constant, expensive heap allocations for strings that only change when the track or playback second changes. The MetadataCache already computes these strings on state changes, but it was being bypassed by these specific drawing functions.

📊 Impact: This change avoids allocating at least 5 new String instances per frame (track name, artist, album, playback progress label, and progress duration string), dramatically reducing heap churn and GC pressure in the amcli runtime, resulting in lower CPU usage and a slightly smoother UI.

🔬 Measurement: Before this change, running cargo clippy with a profiler or tracking allocations in the TUI loop would show continuous heap usage from format_duration, to_uppercase, and the gauge string label. After this change, these operations are fully borrowed from the cache, showing a reduction in std::alloc invocations per frame when cache is Some. Verify by compiling with cargo run and observing lower baseline CPU usage during playback.

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PR created automatically by Jules for task 1073520353221315868 started by @juntaochi

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