fix: resolve all ESLint errors in Vue components

Fixed 22 ESLint errors across 26 Vue component files:
- Removed TypeScript type annotations from ReadingProgress.vue (converted to JS)
- Removed unused variables, imports, and duplicate function declarations
- Fixed HTML parsing errors (invalid attribute names, unclosed tags)
- Added missing :key directives to v-for loops
- Fixed duplicate object keys (backgroundImage)
- Replaced special characters in comments to avoid parsing issues
- Fixed malformed HTML tags (v-else", 003e attributes)

All warnings were left unchanged as requested. Build now passes with 0 errors.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

docs/.vitepress/theme/components/appendix/concurrency-models/ConcurrentVsParallelDemo.vue

@@ -91,7 +91,7 @@
 
         <div class="task-timeline">
           <div
-            v-for="(task, idx) in demoTasks"
+            v-for="task in demoTasks"
             :key="task.id"
             class="task-row"
           >
@@ -184,7 +184,7 @@
 </template>
 
 <script setup>
-import { ref, computed } from 'vue'
+import { ref } from 'vue'
 
 const demoMode = ref('concurrent')
 const isRunning = ref(false)