feat!: convert to ESM on current @actions majors

[janakiram7755]

First change on top of the extracted history.

• type: module, tsconfig nodenext, .js extensions on relative imports. Output is real ESM — 0 require() calls.
• All six @actions/* deps to current majors. Their API surface is unchanged across the bump, so no call sites moved.
• @octokit/webhooks-definitions → @octokit/webhooks-types (the former is deprecated and has no exports map, so nodenext cannot resolve its subpath).
• Dropped an unused @azure/abort-controller import and the dep with it.
• Guarded head.repo.name, now correctly typed optional — previously undefined could be added to restoreRepos.
• Inlined tsconfig, added .gitignore (the extraction inherited neither), dropped src/test.ts.

Cache versions are byte-identical to published 1.4.13 across 10 path/compression/cross-os/cross-arch combinations, so nothing already in the fleet is orphaned.