docs: clean up continue.md section ordering and stale TODOs

- Fix section numbering (was 1,2,3,5,4, now sequential)
- Remove stale dump_simulation_state NULL check TODO (already fixed)
- Retain OrbitalMetrics::angular_position 2D-only TODO for future session

continue.md

@@ -32,3 +32,6 @@
 - Copy from `old_tests/` to `tests/`, rewrite, rebuild, verify.
 - **Always ask for review** before moving to the next file.
 - **Only commit when asked.**
+
+## 5. Testing Harness TODOs
+- [ ] `OrbitalMetrics::angular_position` — uses `atan2(y, x)` which is XY-plane only; meaningless for inclined orbits