refactor_file_moves

Summary

The extension should watch for file moves and renames, migrate the index for moved
. rq files, and update imports and path references both inside the moved file ( outbound )
and in other files that pointed at it ( inbound ), including comment paths in code files.
There should be a single prompt per batch asking whether to apply path updates,
aligned with move_file and rename_file.
Implemented by register-file-mutation-hooks.ts, file-move-plan.ts, file-mutation-gate.ts, file-path-rewrite.ts, and reqlan-path-references.ts.

Jump to outbound references

Jump to inbound references