Handoff: green-light script, reconciled figures, a smaller first step for the decoder

Prepares session 4 for handoff. No new measurements; this reconciles the docs
with what session 4 changed and makes the next session's entry point cheaper.

- tools/bench/check.sh re-runs both display regression tests from the Blu-ray in
  ~40 s and prints ALL GREEN. Verified green cold, after wiping tmp/ and
  re-extracting. STATUS and README both open with it, because everything
  downstream assumes the display path is pixel-exact and nothing previously
  checked that in one command.

- Reconciled the figures session 4 invalidated. Session 3's 38.88 dB ceiling is
  struck through in STATUS with a pointer to 40.81; the "three facts the player
  must honour" table no longer quotes R20 = 0x0116, which was the 768-wide IPL
  timing and would have been copied into the player as if it were the shipping
  value. crtc_mode.lua is now named as the single source of truth for CRTC
  registers, in both STATUS and README.

  The 38.88 dB in the session-3 reproduce section is left alone and annotated
  instead: it is correct for that test, which still packs I = 1. The two numbers
  disagree for a reason and a reader should be able to see which is which.

- Next-step 2 now leads with something smaller than "write the decoder": a dumb
  full-frame RAM->GVRAM blit in 68000 code, timed. That number alone confirms or
  kills the 38% estimate, and needs no bitstream, codebooks, or DLX1 parsing.
  The reference image and its checker already exist.

- Parked the user's Cliff Hanger / Lupin III follow-on in STATUS so it is not
  lost and not mistaken for scheduled work. Cheaper than this project on every
  axis except media prep, which is where it would actually stall.

Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6

README.md

@@ -6,6 +6,9 @@ This is fundamentally a **video codec problem**, not a game-logic problem: the
 game logic is a scene table with branching input windows; the difficulty is
 pushing ~22 minutes of Don Bluth animation through a 10MHz 68000.
 
+**Green-light check:** `./tools/bench/check.sh` (~40 s, needs the Blu-ray
+mounted) re-runs both display regression tests and prints `ALL GREEN`.
+
 ## Read first
 - **`docs/FINDINGS.md`** — measured hardware facts, content statistics, codec
   decision, and a section on measurement traps that produced three separate
@@ -23,7 +26,10 @@ docs/            findings, status, hardware reference
 tools/analysis/  measurement scripts, numbered in the order they were written
                  (01/02 marked BROKEN deliberately, kept as regression refs).
                  Run from the repo root — they import from tools/encoder/.
-tools/bench/     MAME Lua injection harness + 68000 benchmark sources
+tools/bench/     MAME Lua injection harness + 68000 benchmark sources.
+                 `check.sh` re-runs both display regression tests (~40 s).
+                 `crtc_mode.lua` is the single source of truth for CRTC R00-R08
+                 and R20 — do not write CRTC values anywhere else.
 tools/vasm/      vasm m68k assembler (built from source)
 tools/encoder/   hybrid VQ encoder + DLX1 container writer (working)
 src/player/      68000 player (not yet written)