Fix stale post-widen deck-reflow figures (90/144/1190px) across docs and tests, and split test_deck_groups.cpp's width-budget fixtures into a new file.

docs/TODO.md

@@ -365,7 +365,7 @@ The within-deck stacking idea is retired, not deferred.
 **The measured-geometry block that used to live here has been deleted, not moved.** It was
 taken at the 840 px floor with `kDeckCellW = 48` and is wrong twice over — Θ-W6-T1 changed
 both the floor (980) and the cell metrics (60 × 74). The current, re-derived geometry — every
-group's width, both row totals, and the resulting 1190 × 680 floor — is the table in
+group's width, both row totals, and the resulting 1198 × 680 floor — is the table in
 `docs/product/instrument-control-surface.md` §1.2. **Do not resurrect the old numbers.**
 The unresolved 864-vs-872 px VELOCITY↔VOICE adjacency-threshold discrepancy is retired with
 them; it was measured against a layout that no longer exists.