[newbie-contributor] New contributor docs review — quick-setup flags do not exist

## Summary
The documented quick-setup options include flags that are not implemented by `scripts/quick-setup.sh`. A new contributor following the docs can hit an immediate `Unknown flag` failure on the recommended setup path.

## Findings

### 1. Quick-setup docs reference unsupported flags

**Where:**
- `gh-agent-workflows/README.md` (Quick setup script section, line 63: `--skip-secret`)
- `README.md` (Quick setup script section, line 40: `--set-secret`)
- `scripts/quick-setup.sh` (option parser and help, lines 33-60, only supports `--repo`, `--branch`, `--workflows`, `--continuous-improvement`, `--dry-run`)

**Problem:**
The docs and script comments mention `--skip-secret` / `--set-secret`, but the script does not accept either flag. Reproducing with a fresh checkout:

```bash
bash scripts/quick-setup.sh --skip-secret --dry-run
# Unknown flag: --skip-secret

bash scripts/quick-setup.sh --set-secret --dry-run
# Unknown flag: --set-secret
```

**Impact:**
New contributors who follow the documented quick-setup path and use these flags receive an immediate hard failure before setup proceeds, creating avoidable onboarding friction in the primary installation flow.

**Suggested fix:**
Align docs and script behavior by either:
1. Removing/rewriting references to `--skip-secret` and `--set-secret` in contributor-facing docs and script header comments, or
2. Adding backward-compatible no-op handling for those flags with a deprecation notice.

## Suggested Actions

- [ ] Update `gh-agent-workflows/README.md` and root `README.md` to only document flags implemented by `scripts/quick-setup.sh`.
- [ ] Update `scripts/quick-setup.sh` header usage comment to match the actual accepted options.

---
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> - [x] expires on Sep 21, 2026, 11:20 AM UTC

Review the Quick setup sections in gh-agent-workflows/README.md and README.md alongside the option parser and header usage in scripts/quick-setup.sh. Reproduce both documented commands with --dry-run, then align the documented and accepted options and verify the quick-setup commands no longer fail with Unknown flag.

Written by the indexing model from the issue text.