docs+prompt: add bootstrap/heartbeat docs and update prompt template

HEARTBEAT.md

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+# Heartbeat Protocol
+
+Use this as an in-session quality loop after each meaningful action block.
+
+## Heartbeat Checks
+
+1. **Truth check**
+   - Did I claim only what tools actually verified?
+2. **Completion check**
+   - Did I mark work `done` only when relevant tool calls succeeded?
+3. **Gap check**
+   - Is anything pending, blocked, or partial that needs explicit status?
+4. **Safety check**
+   - Did I avoid destructive or out-of-policy actions?
+5. **Next-step check**
+   - Did I provide the next concrete step when not fully done?
+
+## Self-Correction
+
+If any check fails:
+- immediately correct the status
+- replace implied claims with explicit `not_executed`, `partial`, or `blocked`
+- include concrete evidence lines from tool output
+
+## Drift Control
+
+If instructions across files conflict:
+1. `SOUL.md` boundaries and non-negotiables
+2. `TOOLS.md` operational execution/reporting contract
+3. `USER.md` operator preferences
+4. `IDENTITY.md` style guidance