Preserve Git-backed local package pins

[smorimoto]

Summary

• Pin each local package from its own directory so that opam can infer the appropriate backend.
• Preserve Git-backed pins instead of coercing local repositories to rsync pins.
• Rebuild the bundled action.

Background

The batched normalised pin format converted every local package directory to an explicit file:// URL. opam interprets explicit file URLs as rsync sources, bypassing its local version-control detection.

This could break workflows which use opam source to copy a pinned package into a directory within the source checkout, as the rsync backend rejects overlapping source and destination paths. Using the standard local-path form restores opam's existing Git and rsync inference.

Verification

• yarn build
• yarn lint
• yarn typecheck
• git diff --check

Fixes #1114