ci: add focusmode launch evidence gates

[raymondware]

Summary

• Align F006/F013 with the documented lualine component-table contract instead of expecting a bare callable
• Add a deterministic scripts/run-headless-tests.py sweep that fails on stderr assertion/error text, not only Neovim exit code
• Add GitHub Actions launch-evidence CI plus docs/release-evidence.md

Verification

• ./init-test.sh
• python3 scripts/run-headless-tests.py
• git diff --check origin/main..HEAD
• git diff --cached --check before commit
• targeted changed-file secret-value scan: 0 hits
• CI workflow static marker check passed

Guardrails

• No release/tag, branch-protection mutation, publication, external post/outreach, provider mutation, paid action, merge/close, branch deletion, or main push was performed.