Upload only changed gist files

[ryanw13]

Short description of what this resolves:

Fixes #508 by comparing local settings against gist contents and sending a GitHub gist PATCH payload containing only changed files plus deletion markers for removed files.

Changes proposed in this pull request:

• Adds reusable gist comparison helpers for changed and deleted file detection
• Updates upload flow to detect remote-only files as deletions instead of treating the gist as current
• Shows only uploaded/changed files in the upload summary, with deleted gist files listed separately

Fixes: #508

How Has This Been Tested?

• Reviewed the upload path statically against the existing gist PATCH flow.
• Verified the working tree from a Docker container with networking disabled and a read-only mount of this repository.
• Full TypeScript/test execution was not run because the repository does not include a lockfile, and installing dependencies would require an unsafe dependency install.

Screenshots (if appropriate):

N/A

Checklist:

• I have read the contribution guidelines.
• My change requires a change to the documentation and GitHub Wiki.
• I have updated the documentation and Wiki accordingly.