Add nested copilot-sdk directory (embedded repo)

[ncamaraljr7219]

Why

This PR persists a previously untracked nested 'copilot-sdk/' git checkout that was present in the working tree. The user requested the branch be pushed and a pull request opened.

What changed

• Adds a gitlink entry for the nested 'copilot-sdk' directory (create mode 160000). No other files modified.

Notes for reviewers

• This records an embedded repository (gitlink). Clones of the outer repository will not include the nested repo contents; they will only contain a gitlink reference.
• If this was accidental, consider removing it (git rm --cached copilot-sdk) and adding it to .gitignore, or convert it to a proper submodule using 'git submodule add'.
• No runtime or behavioral changes included; this is an additive commit to persist local state.

N/A