feat(themes): #62 whole-swap CSS self-containment CI gate

Add tools/check-theme-wholeswap.py and checks.theme-wholeswap: every
themes/*/waybar.css must @define-color each @name it references (raw
readFile, no palette prepend — neon-glass class), and every preset needs
preview.png + non-empty backgrounds/. README: four waybar.css themes
(drop quarantined neon-glass). Close #62.

Verified: V0 (script + negative fixture + checks.theme-wholeswap + flake check --no-build).

agent/JOURNAL.md

@@ -17,6 +17,17 @@ Template:
 
 ---
 
+## 2026-07-10 — #62 whole-swap CSS self-containment CI gate
+- **Task:** NEXT #62 — cheap gate that waybar.css defines every @color it
+  references (would have caught neon-glass) + preview/backgrounds present.
+- **Did:** `tools/check-theme-wholeswap.py` + `checks.theme-wholeswap` in
+  flake.nix. README: five themes → four (drop quarantined neon-glass).
+  Closed #62.
+- **Verified:** **V0** — script OK on themes/ (24 presets, 4 whole-swaps);
+  negative fixture with `@text`/`@base` and zero defines fails as expected;
+  `nix build .#checks.x86_64-linux.theme-wholeswap` green.
+- **Next suggestion:** #59 NVIDIA install comments, or #60 BAT*-agnostic.
+
 ## 2026-07-10 — #61 Review Source line tracks offline/online
 - **Task:** NEXT #61 — Review panel Source must match the cache.nixos.org
   probe (`OFFLINE`), not always claim “no network needed”.