fix: improve SEO with pre-rendering and dynamic meta tags

Critical SEO improvements to fix Google Search Console indexing:

## Sitemap Updates:
- Added missing Invoice Editor and What's New pages
- Updated all lastmod dates to 2025-10-15
- Increased editor tools priority to 0.9
- Added organizational comments
- Fixed /whats-new route (was /release-notes)

## Pre-rendering Implementation:
- Added react-snap for static HTML generation
- Configured to pre-render all tool pages
- Solves React SPA indexing issue
- Crawlers now see full HTML content

## Dynamic Meta Tags:
- Added react-helmet-async for SEO management
- Created reusable SEO component with:
  - Dynamic titles and descriptions
  - Open Graph tags (Facebook)
  - Twitter Card tags
  - JSON-LD structured data
  - Canonical URLs
- Wrapped App with HelmetProvider
- Added SEO to Home page

## Route Fixes:
- Added /whats-new route (primary)
- Kept /release-notes as fallback
- Consistent routing across app

## Documentation:
- Created comprehensive SEO_FIX_GUIDE.md
- Step-by-step Google Search Console instructions
- Troubleshooting guide
- Timeline expectations
- Testing procedures

These changes will dramatically improve Google indexing and search visibility.

package.json

@@ -32,8 +32,10 @@
     "react": "18.3.1",
     "react-diff-view": "^3.3.2",
     "react-dom": "18.3.1",
+    "react-helmet-async": "^2.0.5",
     "react-router-dom": "6.26.2",
     "react-scripts": "5.0.1",
+    "react-snap": "^1.23.0",
     "reactflow": "^11.11.4",
     "serialize-javascript": "^6.0.0",
     "web-vitals": "^2.1.4"
@@ -46,10 +48,36 @@
   },
   "scripts": {
     "start": "react-scripts start",
-    "build": "react-scripts build",
+    "build": "react-scripts build && react-snap",
+    "build:no-snap": "react-scripts build",
     "test": "react-scripts test",
     "eject": "react-scripts eject"
   },
+  "reactSnap": {
+    "inlineCss": true,
+    "minifyHtml": {
+      "collapseWhitespace": false,
+      "removeComments": false
+    },
+    "puppeteerArgs": [
+      "--no-sandbox",
+      "--disable-setuid-sandbox"
+    ],
+    "include": [
+      "/",
+      "/object-editor",
+      "/table-editor",
+      "/invoice-editor",
+      "/url",
+      "/base64",
+      "/beautifier",
+      "/diff",
+      "/text-length",
+      "/whats-new",
+      "/privacy",
+      "/terms"
+    ]
+  },
   "eslintConfig": {
     "extends": [
       "react-app",