fix(viewer): replace text-accent with text-primary on annotation toggle inactive state

Fixes WCAG 2.1 AA contrast failure (#341): text-accent (#a1dcd8) on light
PDF control bar was 1.52:1 — well below the 4.5:1 AA minimum. text-primary
resolves to #012851 in light mode (14.5:1) and #a1dcd8 in dark mode (9:1) —
both states pass AA in both themes.

Adds PdfControls.svelte.spec.ts with 5 tests covering toggle visibility,
label strings, and the contrast-safe class assertion.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/eslint.config.js

@@ -40,6 +40,26 @@ export default defineConfig(
 				parser: ts.parser,
 				svelteConfig
 			}
+		},
+		rules: {
+			// text-accent resolves to #a1dcd8 in light mode (1.52:1 on white — WCAG fail).
+			// layout.css documents it as decorative-only (borders, icon tints, bg fills).
+			// For any text label use text-primary or text-ink instead. This rule catches
+			// the pattern where text-accent appears inside a JavaScript string literal
+			// (e.g. conditional ternary class expressions in Svelte templates).
+			'no-restricted-syntax': [
+				'error',
+				{
+					selector: 'Literal[value=/\\btext-accent\\b/]',
+					message:
+						'text-accent is decorative-only (#a1dcd8 in light mode = 1.52:1 contrast — WCAG fail). Use text-primary or text-ink-2 for text labels.'
+				},
+				{
+					selector: 'TemplateLiteral > TemplateElement[value.raw=/\\btext-accent\\b/]',
+					message:
+						'text-accent is decorative-only (#a1dcd8 in light mode = 1.52:1 contrast — WCAG fail). Use text-primary or text-ink-2 for text labels.'
+				}
+			]
 		}
 	}
 );