docs(todo): consolidate vehicle investigation into MEMORY.md; mark tasks resolved

- TODO.md: drop the 200+ lines of vehicle-investigation prose (evidence, ruled-out
  list, bisect results) that MEMORY.md already carries, and point the intro at
  MEMORY.md for observations. Mark the three Chaos-rig tasks resolved (plugin
  enablement -> 4 wheels; PhysicsType=Simulated -> simulates/settles/drives).
- AGENTS.md: note that observations belong in MEMORY.md, not TODO.md.

AGENTS.md

@@ -55,7 +55,7 @@ Semantic Versioning: `MAJOR.MINOR.PATCH`.
 
 The two files have separate roles:
 
-- **[TODO.md](TODO.md)** is the single, central task list for all agents: checkbox items, progress marks, and active-section ownership. Put all planned actionable work and follow-ups there. Do not create parallel task lists elsewhere.
+- **[TODO.md](TODO.md)** is the single, central task list for all agents: checkbox items, progress marks, and active-section ownership. Put all planned actionable work and follow-ups there. Do not create parallel task lists elsewhere. Any notes or observations should be recorded in [MEMORY.md](#memory).
 - **[ROADMAP.md](ROADMAP.md)** holds the development plan: milestone goals, scope, decisions, and release gates for each version. It is a planning document and contains **no checkbox items**. Read it for future direction; record scope changes there as prose, and record the resulting tasks in `TODO.md`.
 
 Rules for `TODO.md`: