fix(github): bind repo grants KV namespace

[tlgimenes]

Summary

• Bind the GitHub MCP REPO_GRANTS KV namespace to the real Cloudflare namespace id.
• Fixes the deploy workflow failure caused by the placeholder KV namespace id.

Test Plan

• bun test (from github/)
• git diff --check
• CLOUDFLARE_ACCOUNT_ID=c95fc4cec7fc52453228d9db170c372c bunx wrangler deploy --dry-run --outdir=dist

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Summary by cubic

Bind the GitHub MCP REPO_GRANTS KV namespace to the real Cloudflare ID to unblock deployments. Replaces the placeholder in github/wrangler.toml so the deploy workflow stops failing.

^{Written for commit de38c4a. Summary will update on new commits.}