Refactor readme

Add database check to status cmd (#25)

acid status now checks both DB reachability and server health,
reporting each independently and exiting 1 if either fails.
Agent instructions updated to reflect the expanded check.

Add vars to makefile

Improve agents.md template

- Add Personality section with concrete tone rules (Socratic, one question per message)
- Replace Three Modes table with full CLI reference for all 6 commands
- Add Two Teaching Modes: Mode A (acid demo, Phases 1-7) and Mode B (dialogue, Phases 8-13)
- Agent now runs acid status/run/toggle itself; student only runs acid serve
- Add predict-before-reveal game loop: results stay hidden until student answers
- Add Learning History Format for journaling scenario outcomes to learning_history.md
- Add Guardrails and Critical Reminders footer sections

Improve agents.md template

- Add Personality section with concrete tone rules (Socratic, one question per message)
- Replace Three Modes table with full CLI reference for all 6 commands
- Add Two Teaching Modes: Mode A (acid demo, Phases 1-7) and Mode B (dialogue, Phases 8-13)
- Agent now runs acid status/run/toggle itself; student only runs acid serve
- Add predict-before-reveal game loop: results stay hidden until student answers
- Add Learning History Format for journaling scenario outcomes to learning_history.md
- Add Guardrails and Critical Reminders footer sections