Add branding options and Twitter handle support

[shigahi]

Summary

This PR implements Issue #18 (Replace Notion branding) and Issue #19 (Add Twitter/X handle for social cards).

Changes

Issue #18: Replace Notion branding with custom site name

• Added Site Name field in Advanced Settings → Branding & Social
  • Used for og:site_name meta tag
  • Falls back to domain if not specified
• Added Brand Replacement field
  • Replaces "Notion" text in meta tag content
  • Useful for removing Notion branding from search results and social shares

Issue #19: Add Twitter/X handle for social cards

• Added Twitter/X Handle field
  • Injects twitter:site and twitter:creator meta tags
  • Improves attribution when content is shared on Twitter/X

UI Changes

New fields added under Advanced Settings → Branding & Social section:

• Site Name (placeholder: "My Awesome Site")
• Brand Replacement (placeholder: "My Brand")
• Twitter/X Handle (placeholder: "@username")

Generated Worker Code

The following configuration is now included in generated worker scripts:

const SITE_NAME = 'My Awesome Site';
const BRAND_REPLACEMENT = 'My Brand';
const TWITTER_HANDLE = '@username';

Testing

• Build passes locally
• New fields appear in Advanced Settings
• Generated worker code includes new configuration
• MetaRewriter correctly replaces og:site_name and Notion branding
• HeadRewriter correctly injects Twitter meta tags

Closes #18
Closes #19