chore: prepare RowBridge 0.6.1 release

[SerDrozd]

Summary

Prepare RowBridge 0.6.1 with clearer public documentation, small UI consistency fixes, and reproducible CI references.

Changes

• rewrite the README around the actual user workflow and current product behavior
• clarify matching documentation, including score-ordered one-to-one selection
• clean up the changelog and remove development-stage wording
• make upload limits consistent across both input panels
• simplify the error-page action
• replace milestone-based static asset cache keys with the package version
• pin GitHub Actions to immutable commit SHAs
• bump the package and lockfile to 0.6.1

Validation

• uv sync --extra dev --locked
• uv run ruff check .
• uv run mypy src tests
• uv run pytest — 50 passed
• uv build
• git diff --check