✨ Add fastapi cloud setup-ci

[savannahostrowski]

Closes https://github.com/fastapilabs/cloud/issues/2832

Some notes on the UX:

Preconditions (exit early if not met)

• User must be logged in and app must be configured (i.e. already have a .fastapicloud/cloud.json) --> otherwise, users will see a message to log in or run fastapi deploy.
• Git remote origin must exist and be a GitHub URL --> otherwise error

Happy Path UX

1. Detect context — reads repo slug from git origin, detects default branch via git symbolic-ref refs/remote/origin/HEAD (falls back to main if the command fails)
2. Display summary — shows repo and branch
3. --dry-run — optional but if passed, prints what would happen and exits
4. Create deploy token — calls the API to create (or regenerate if one already exists) a token named GitHub Actions — owner/repo
5. Set GitHub secrets — two paths:
   • gh CLI available: sets FASTAPI_CLOUD_TOKEN and FASTAPI_CLOUD_APP_ID as repo secrets via gh secret set
   • gh CLI not found: prints the token value and app ID with a link to the repo's secrets page for manual setup
6. Write workflow file (skipped with --secrets-only):
   • If deploy.yml already exists (and no --file flag): prompt to overwrite, enter a new name, or skip
   • If --file passed: writes to .github/workflows/<name>
   • Otherwise: writes to .github/workflows/deploy.yml
7. Done! Show expiry date and reminds the user to regenerate before it expires

Available Flags:

• --branch / -b — override deploy branch (default: main)
• --secrets-only / -s — skip writing the workflow file, just set the secrets in the repo
• --dry-run / -d — preview without changes
• --file / -f — custom workflow filename

[patrick91]

This is great, I left some comments, but I'm excited to see this in soon!