Prepare Sharp Frames v0.4.0

[shrimbly]

What changed

• harden frame extraction, sharpness analysis, selection, saving, cancellation, and cleanup
• add resolution-normalized focus scoring and improved temporal selection quality
• add a scrollable, keyboard-accessible full-frame timeline and refine the configuration/selection UI
• add cross-platform CI for Linux, macOS, and Windows on Python 3.10 through 3.13
• expand regression coverage for runtime failures, selection consistency, output collisions, and UI behavior
• prepare the package, changelog, and release notes for Sharp Frames 0.4.0

Why

The processing and selection pipelines had accumulated inconsistencies between preview and execution, incomplete failure reporting, fragile subprocess cleanup, and limited coverage of platform-specific behavior. This release makes those paths deterministic and testable while improving the frame-selection experience.

User impact

Users get more consistent sharp-frame selection across image resolutions, clearer failure reporting, safer output handling, and a timeline that can display and navigate the complete analyzed frame set. Windows users also gain explicit CI coverage and platform-aware FFmpeg handling.

Validation

• venv/bin/python -m pytest -q — 327 passed
• venv/bin/python -m build --wheel --outdir /tmp/sharp-frames-release-wheel
• git diff --check

Release checklist

• Linux CI passes
• macOS CI passes
• Windows CI passes
• Merge to develop, then promote the release commit to master
• Create and push annotated tag v0.4.0 from the final master release commit
• Publish the GitHub release using RELEASE_NOTES.md
• Publish sharp-frames==0.4.0 to the package index, if applicable