fix: link repair targets to source repo

[stainlu]

Summary:

• Link shorthand repair targets like #123 through the run record's source repo.
• Keep full GitHub issue/PR URLs labeled as their issue number.
• Add fixture coverage for repair dashboard target links.

Verification:

• pnpm run check
• pnpm run render -- --source /private/tmp/clawsweeper-state-latest --output /private/tmp/clawsweeper-state-rendered-repair-links.md
• rg -n '](#[0-9]+)' /private/tmp/clawsweeper-state-rendered-repair-links.md returned no matches