Add Cache-Control header optimization

[shigahi]

Summary

Add configurable Cache-Control headers to improve performance and reduce origin requests.

Changes

• Add CachingOptions interface with htmlTtl, staticAssetsTtl, imageTtl
• Add applyCacheHeaders function to set Cache-Control based on content type
• Apply cache headers to JS, CSS, images, and HTML responses
• Add "Cache-Control Headers" section in Advanced Settings UI

Implementation Details

Cache headers are applied based on content type:

• Static assets (JS, CSS, fonts): public, max-age={TTL}, immutable
• Images: public, max-age={TTL}
• HTML pages: public, max-age={TTL}, stale-while-revalidate=60

Default TTL values:

• HTML: 60 seconds
• Static assets: 86400 seconds (1 day)
• Images: 604800 seconds (1 week)

UI Changes

Added "Cache-Control Headers" section with:

• Enable/disable toggle
• HTML Page TTL input
• Static Assets TTL input
• Image TTL input

Benefits

• Faster page loads for returning visitors
• Reduced bandwidth costs
• Better Lighthouse performance scores
• Less load on Notion servers

Closes #33