Rewrite reference docs as current state; record the style rule

Reference, guidelines and plan documents describe what is and what will be.
Retirement stories, resolved-risk narration and against-the-alternative
argument moved out or were cut; reports keep that material.

What survives the cut is the mechanism that can bite again (driving side is a
country-level property) and the condition that would change a decision (a
permanently installed, car-powered panel), both stated generally.

Also removes a duplicated Japan section from a bad edit.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013kj58Jugkic783b8ZrtTVZ

docs/ROADMAP.md

@@ -59,9 +59,6 @@ Order chosen by feedback speed, not ambition.
       quickest to iterate on, and is the only display in current scope
 - [ ] `app-esp32` — RLCD/e-ink glanceable subset. Deferred, no hardware in scope
 
-Video out was dropped along with `app-hud`; see the display contract in
-[ARCHITECTURE.md](ARCHITECTURE.md#display-contract).
-
 ## Phase 5 — Camera and inference · *separate task*
 
 Deliberately deferred. It is the reason the compute is a Jetson rather than a