docs(prompts): add Wren delegate agent prompt and delegation policy

[rthomazel]

Adds two things:

• wren-delegate.md — full system prompt for Wren, a delegate subagent for bounded tasks (codebase discovery, log analysis, schema inspection, running tools, formatting)
• chat-work-session-jail.md — new # Delegation section telling Woody when to delegate vs. handle inline

Wren prompt design decisions:

• Python file editing pattern near the top (load-bearing, earns the space)
• All constraints framed as → Escalate triggers, not forbidden zones
• Hard output delimiter ban: response must begin and end with ---, no preamble or postamble
• No PHI/PII section (not relevant to our codebases)