feat: optimize SEO based on GSC data

- Fix broken hreflang: /en/ ghost page removed, all hreflang point to canonical /
- Add canonical URL tag
- Remove emoji from page titles
- Rewrite title/description with target keywords (LaTeX OCR, math formula recognition, handwriting math)
- Add JSON-LD WebApplication structured data schema
- Update og:image to clean URL without OSS params, add og:image dimensions
- Fix favicon reference from vite.svg to favicon.png
- Add public/sitemap.xml with hreflang annotations
- Add public/robots.txt pointing to sitemap
- Update seoHelper.ts keywords for both zh/en to match search intent
- Add CLAUDE.md project documentation

src/lib/seoHelper.ts

@@ -8,14 +8,14 @@ interface SEOContent {
 
 const seoContent: Record<Language, SEOContent> = {
   zh: {
-    title: '⚡️ TexPixel - 公式识别工具',
-    description: '在线公式识别工具，支持印刷体和手写体数学公式识别，快速准确地将图片中的数学公式转换为可编辑文本。',
-    keywords: '公式识别,数学公式,OCR,手写公式识别,印刷体识别,AI识别,数学工具,免费,混合文字识别,texpixel,TexPixel',
+    title: 'TexPixel - AI 数学公式识别工具 | LaTeX、MathML OCR',
+    description: '免费 AI 数学公式识别工具，支持手写和印刷体公式识别，一键将图片或 PDF 中的数学公式转换为 LaTeX、MathML 和 Markdown 格式。',
+    keywords: '数学公式识别,LaTeX OCR,手写公式识别,公式转LaTeX,数学OCR,MathML转换,手写方程识别,公式识别,数学公式OCR,texpixel',
   },
   en: {
-    title: '⚡️ TexPixel - Formula Recognition Tool',
-    description: 'Online formula recognition tool supporting printed and handwritten math formulas. Convert images to LaTeX, MathML, and Markdown quickly and accurately.',
-    keywords: 'formula recognition,math formula,OCR,handwriting recognition,latex,mathml,markdown,AI recognition,math tool,free,texpixel,TexPixel,document recognition',
+    title: 'TexPixel - AI Math Formula Recognition | LaTeX, MathML OCR Tool',
+    description: 'Free AI-powered math formula recognition tool. Convert handwritten or printed math formulas in images to LaTeX, MathML, and Markdown instantly. Supports PDF and image files.',
+    keywords: 'math formula recognition,LaTeX OCR,handwriting math recognition,formula to latex,math OCR,MathML converter,handwritten equation recognition,texpixel',
   },
 };