ci: fail on references to undefined CSS custom properties

A typo'd CSS custom property (e.g. var(--pg-input-normal-hover) where the
real token is --pg-input-hover) does not error — it silently falls back to
currentColor or an invalid value — so it slips through review. This adds a
stylelint check that flags any var(--…) pointing at a token that is never
defined, and wires it into the Lint CI job (npm run lint:css).

The check is intentionally scoped to the single
csstools/value-no-unknown-custom-properties rule (no base config) so it
only guards this bug class without a noisy retrofit. The --pg-* tokens live
in global.scss, whose SCSS syntax the plugin's importFrom loader can't
parse, so the config parses that file with postcss-scss and feeds the
resolved token set to the plugin inline (stays in sync automatically).

Enabling it surfaced five pre-existing undefined tokens, all fixed here
(intended values recovered from git history):

  --pg-input-normal-hover  -> --pg-input-hover        (input :hover border)
  --pg-primary-rgb         -> defined as 48, 149, 222 (RGB of --pg-primary)
  --pg-hard-background     -> --pg-general-background (was originally `white`)
  --pg-input-normal-light  -> --pg-input-normal       (file-row separators)

These were rendering wrong (transparent/invalid/currentColor); the fixes
restore the intended appearance.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: rubenhensen

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
       - run: npx svelte-kit sync
       - run: npx svelte-check --threshold warning
 
-  # Run prettier --check and eslint.
+  # Run prettier --check, eslint, and stylelint.
   lint:
     name: Lint
     runs-on: ubuntu-latest
@@ -44,6 +44,8 @@ jobs:
       - run: npm ci
       - run: npx svelte-kit sync
       - run: npm run lint
+      # Fail on references to undefined CSS custom properties (e.g. typo'd --pg-* tokens).
+      - run: npm run lint:css
 
   # Create a GitHub release (and tag) when conventional commits warrant one.
   release-please: