Explain generated infrastructure PRs clearly

[davejohnson]

What changed

• Generated infrastructure PRs now explain each workflow, template, and settings-file change in plain language.
• Deployment PRs identify the services and provider, exact commit pinning, retry and verification behavior, saved evidence, and whether merging may deploy.
• Exact filenames remain available in a collapsible technical section.

Why

PR #59 showed that the old generic description did not tell a vibe coder what Hypervibe was actually changing or what would happen after merge.

Safety

• Existing open PR descriptions are not overwritten.
• Generated PRs still contain no secret values.
• Hypervibe still never merges generated infrastructure PRs automatically.

Checks

• 67 focused tests passed
• npm run typecheck passed