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/database-intro/BPlusTreeDemo.vue

@@ -190,7 +190,6 @@ const startIndex = () => {
   indexStep.value = 0
   indexSteps.value = ['根节点', '中间节点', '叶子节点']
 
-  const steps = ['根节点 (1-100)', '中间节点 (1-10)', '叶子节点 (找到 7)']
   let currentStep = 0
 
   const interval = setInterval(() => {

docs/.vitepress/theme/components/appendix/database-intro/DatabaseIndexDemo.vue

@@ -1,5 +1,5 @@
 <script setup>
-import { ref, computed } from 'vue'
+import { ref } from 'vue'
 
 const searchQuery = ref(55)
 const isSearching = ref(false)