feat(gates): WP-02 — harden check:tokens to whole-app colour guard

- Move the guard to scripts/check-tokens.sh; regex now catches hex +
  rgb()/hsl() (was hex-only) across ALL src/app components (was three
  ui/layout dirs). `token-ok` marker suppresses justified false positives;
  px stays out of scope (documented in the script).
- Zero exclusions: debug-state's dark code-editor palette moves to
  --app-devpanel-* tokens in styles.scss (the one exempt file), dropping its
  --exclude hole.
- Tokenize remaining hits: site-footer border via color-mix; three brief
  border widths via --rhc-border-width-* (new --rhc-border-width-lg: 3px).

Verified: planted violation fails the guard; GREEN + test-storybook:ci.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app/brief/ui/letter-preview/letter-preview.component.ts

@@ -37,7 +37,7 @@ const SAMPLE_VALUES: Record<string, string> = {
   styles: [`
     :host{display:block}
     .toolbar{display:flex;justify-content:flex-end;margin-block-end:var(--rhc-space-max-sm)}
-    .letter{background:var(--rhc-color-wit);border:1px solid var(--rhc-color-border-default);border-radius:var(--rhc-border-radius-md);padding:var(--rhc-space-max-2xl)}
+    .letter{background:var(--rhc-color-wit);border:var(--rhc-border-width-sm) solid var(--rhc-color-border-default);border-radius:var(--rhc-border-radius-md);padding:var(--rhc-space-max-2xl)}
     section{margin-block-end:var(--rhc-space-max-xl)}
     p{margin:0 0 var(--rhc-space-max-sm)}
     ul,ol{margin:0 0 var(--rhc-space-max-sm);padding-inline-start:1.4em}