Add a new /delegate skill that generates ready-to-paste prompts for delegating parts of a task to other AI agents (Gemini, Cursor, Codex, etc.) during the /start planning gate.

The skill is designed to run during Step 2 of /start — after investigation but before saying go. It uses context already loaded by /start (issue body, agent notes, branch info) to produce a scoped prompt with built-in rules: "do not commit" and "be surgical." Each delegation also tells the lead agent to skip that work when proceeding.

Changes:

• New skills/delegate.md source skill with generated output for all four adapters
• Updated /start Step 2 gates (both Case A and Case B) to mention /delegate as an option
• Added delegate to BRANCH_PROD and BRANCH_DEV used_in lists in config.schema.yaml

Issue #109