fix: enable eslint-plugin-svelte a11y rules and fix violations

.gitignore

@@ -45,6 +45,10 @@ backend/.DS_Store
 # 3. Node/Svelte (Frontend)
 # ------------------------------------
 
+# Root-level npm artifacts (from nested npm installs)
+node_modules/
+package.json
+
 # Dependencies
 frontend/node_modules
 

frontend/eslint.a11y.config.js

@@ -9,6 +9,17 @@ import svelteConfig from './svelte.config.js';
 
 const gitignorePath = fileURLToPath(new URL('./.gitignore', import.meta.url));
 
+// Svelte 5 a11y checking — no separate svelte/a11y-* rules exist in
+// eslint-plugin-svelte v3.20.0.  All a11y validation is built into the
+// Svelte 5 compiler itself (42 checks covering alt-text, ARIA, keyboard
+// interaction, semantic HTML, tabindex, roles, labels, etc.).  The
+// svelte/valid-compile rule below surfaces EVERY compiler warning — including
+// all compiler-level a11y diagnostics — as ESLint errors.
+//
+// See node_modules/svelte/src/compiler/warnings.js for the full list of
+// a11y_* warning codes.  No separate eslint-plugin-a11y or jsx-a11y rules
+// are needed since the Svelte 5 compiler covers them natively.
+
 export default defineConfig(
 	includeIgnoreFile(gitignorePath),
 	js.configs.recommended,
@@ -34,10 +45,11 @@ export default defineConfig(
 		name: 'svelte:a11y:rules',
 		files: ['**/*.svelte', '**/*.svelte.ts', '**/*.svelte.js'],
 		rules: {
-			// Compile all .svelte files and surface compiler warnings as ESLint errors.
-			// The Svelte 5 compiler has built-in a11y checks (a11y_missing_attribute,
-			// a11y_click_events_have_key_events, a11y_no_static_element_interactions, etc.)
-			// that are enabled by default via accessibilityWarnings: true.
+			// Surface ALL Svelte 5 compiler warnings as errors — this catches every
+			// built-in a11y check (a11y_missing_attribute, a11y_click_events_have_key_events,
+			// a11y_no_static_element_interactions, a11y_role_has_required_aria_props,
+			// a11y_label_has_associated_control, a11y_media_has_caption, … 42 total).
+			// No warning filter is applied, so every diagnostic is reported.
 			'svelte/valid-compile': 'error',
 
 			// Require explicit type attribute on <button> elements