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/git-intro/GitBranchMergeDemo.vue

@@ -75,6 +75,7 @@
           />
           <circle
             v-for="(c, i) in main"
+            :key="i"
             :cx="60 + i * 50"
             cy="40"
             r="8"
@@ -82,6 +83,7 @@
           />
           <circle
             v-for="(c, i) in feat"
+            :key="i"
             :cx="180 + i * 50"
             cy="80"
             r="8"