feature: add persistent agent memory across session restarts

[benvinegar]

What

Adds persistent, cross-session memory so Baudbot agents retain operational learnings, user preferences, and recurring patterns across session restarts. Currently agents lose all context when sessions restart — they re-learn the same lessons every time.

New files

• pi/skills/control-agent/memory/operational.md — infrastructure learnings, common errors/fixes
• pi/skills/control-agent/memory/repos.md — per-repo build quirks, CI gotchas, architecture notes
• pi/skills/control-agent/memory/users.md — user preferences, timezone, communication style
• pi/skills/control-agent/memory/incidents.md — past incidents: root cause + fix

How it works

1. deploy.sh seeds memory files to ~/.pi/agent/memory/ — only if they don't already exist (agent-owned, never overwritten)
2. setup.sh creates the memory directory during initial setup
3. Control agent reads all memory files on startup (added to startup checklist)
4. Control agent updates memory files as it learns new things (dated Markdown entries)
5. Dev agents read repos.md for repo-specific knowledge before starting work
6. Sentry agent reads incidents.md for past incident context when triaging

Design decisions

• Plain Markdown — no embeddings, no vector search, no file watcher. Files are small enough (<50KB) to include directly in context.
• Agent-owned — memory files are writable by the agent, not protected like security files. Deploy never overwrites existing content.
• No secrets — every memory file has a "DO NOT store secrets" warning. redact-logs.sh can scan these in the future.
• Inspired by OpenClaw — their MEMORY.md + memory/ directory pattern, but without the Tier 2 semantic search infrastructure (SQLite + embeddings + hybrid search). We can add that later if memory grows past ~50KB.

Updated files

• pi/skills/control-agent/SKILL.md — new Memory section + startup checklist
• pi/skills/dev-agent/SKILL.md — reads repos.md before starting work
• pi/skills/sentry-agent/SKILL.md — reads incidents.md on startup
• bin/deploy.sh — seeds memory files (only if missing)
• setup.sh — creates memory directory
• README.md, AGENTS.md — architecture docs