chore(release): prepare v0.8.0

[fcoury]

Why

Prepare Red v0.8.0 from the changes merged since v0.7.0. The generated release files needed a campaign and README pass so the public highlights describe this release rather than repeat v0.7.0.

What changed

• Bump Cargo.toml, Cargo.lock, and the README release references to 0.8.0.
• Add the generated v0.8.0 section to CHANGELOG.md.
• Update release/campaign.toml with directory browsing, mouse selection, shebang syntax detection, picker navigation, and optional Rust Glancer. Preview copy remains unpublished until the release workflow runs.
• Refresh the README highlights and the version labels in the getting-started and Vim-compatibility docs.

How to Test

1. Run python3 scripts/release_campaign.py validate --version 0.8.0 and render all channels; confirm each story shipped after v0.7.0 and the X and Bluesky previews fit their limits.
2. Run python3 scripts/readme_release.py --check and confirm the README version and pinned installer example are 0.8.0.
3. Review the generated changelog against v0.7.0..HEAD; confirm the directory-browser Windows fix and rustls advisory fix are included.
4. Run the Markdown link checker and confirm the release PR's CI, Clippy, runtime self-check, Windows tests, and changelog gate pass.
5. After the draft release is built, verify all four archives, checksums, installers, and announcement copy before publication.

Merging this PR does not publish v0.8.0. Pushing an annotated v0.8.0 tag from the merge commit starts the draft release build.