Improve playback smoothness and release 0.1.15

[Riqqqque]

What changed

• removed playback-time layout measurement and isolated the media element from trim clock rerenders
• enabled ahead buffering and stable native object-fit sizing for normal, theater, and fullscreen layouts
• lowered FFprobe and encoder detection process priority and added fast-start metadata to compatible stream-copy trims
• refreshed compatible dependencies, fixed clean-install lockfile consistency, and repaired CRLF version bumps
• bumped HitPlayer to 0.1.15

Why

Playback should stay on WebView2's hardware-accelerated media path with less UI work around it, especially for 60 fps clips and network-backed media. The release also closes CI, packaging, and trim-startup edge cases found during the full review.

Validation

• npm ci
• npm run build
• cargo fmt --manifest-path src-tauri/Cargo.toml --all -- --check
• cargo clippy --manifest-path src-tauri/Cargo.toml --all-targets --all-features -- -D warnings
• cargo test --manifest-path src-tauri/Cargo.toml --all-targets (30 passed)
• npm audit --audit-level=high (0 vulnerabilities)
• Windows NSIS installer build, silent upgrade, installed launch, and real 1440p60 playback verification