ci: add stub workflow for review.agent discovery

[PureWeen]

Summary

Adds a minimal stub review.agent.lock.yml to main so that GitHub Actions can discover the workflow_dispatch trigger. This enables testing the real review workflow from the feature branch (feat/expert-review-workflow, PR #118) using:

gh workflow run review.agent.lock.yml --ref feat/expert-review-workflow -f pr_number=115

Why this is needed

GitHub requires workflow_dispatch workflows to exist on the default branch before they can be triggered via API/CLI/UI. The real workflow only exists on feat/expert-review-workflow (PR #118).

What it does

• The stub does nothing — it exits with failure if run directly
• It only serves as a discovery placeholder so --ref can dispatch the real workflow
• Once PR feat: add expert code review workflows with 3-model adversarial consensus #118 merges, this stub is replaced by the real compiled workflow

Safe to merge

• permissions: {} — no permissions granted
• The stub job just prints a message and exits 1
• No secrets, no checkout, no tools

[Copilot]

Pull request overview

Adds a minimal placeholder GitHub Actions workflow on main so workflow_dispatch can be discovered, enabling gh workflow run ... --ref <branch> to execute the real workflow defined on a feature branch (per PR #118).

Changes:

• Introduces a stub review.agent.lock.yml with a workflow_dispatch trigger and pr_number input.
• Adds a single stub job that prints guidance and exits non-zero to prevent accidental direct use.

[Copilot]

workflow_dispatch inputs don't support type: number (supported types are typically string (default), boolean, choice, environment). Using an unsupported type can make the workflow invalid and prevent GitHub from discovering/dispatching it. Suggest removing type: entirely (defaults to string) or switching to type: string and letting the caller pass numeric text.

Suggested change

	type: number
	type: string

[PureWeen]

Re: Copilot suggestion to change type: number to type: string

Not a valid concern — type: number is a supported workflow_dispatch input type (alongside string, boolean, choice, and environment). It was added to GitHub Actions after the original four types.

The real workflow on feat/expert-review-workflow and the gh-aw compiled lock file both use type: number for this input, and the compiler accepted it without warnings. The stub should match the real workflow's schema to ensure consistent behavior when dispatching with --ref.