Support MT.DELETE.<filename> marker files in shared-overwrite for file deletion

[Copilot]

When a file previously deployed via shared-overwrite needs to be removed from target repos, there was no mechanism to do so — the file would persist indefinitely.

Changes

• deleteFile() function — added to both code_setup.sh and sync.sh; removes the target file if present, skips gracefully if not
• deployDirectory() — checks for MT.DELETE.* filename pattern before normal deploy logic; strips the MT.DELETE. prefix to resolve the target path and calls deleteFile
• shared-overwrite top-level loop — same MT.DELETE.* check applied for files directly in shared-overwrite/ (not just nested ones)

Behavior

A file at shared-overwrite/.github/actions/setup/MT.DELETE.action.yml causes .github/actions/setup/action.yml to be deleted in the target repository:

shared-overwrite/
└── .github/
    └── actions/
        └── setup/
            └── MT.DELETE.action.yml   →  deletes .github/actions/setup/action.yml in target

[gemini-code-assist]

Code Review

This pull request introduces a deleteFile function to both code_setup.sh and sync.sh to support deleting files identified by the MT.DELETE.* prefix during deployment. The review feedback recommends centralizing the deleteFile implementation into a common script to reduce duplication and removing redundant checkResult calls, as the function already performs internal error checking.