fix(pagestream): opaque cards, inline browsing, remove blue border, scroll fixes
- Replace translucent rgba backgrounds with opaque var(--base01/02/03) for cards, search, navbar
- Remove backdrop-filter blur from cards and inputs
- Remove scale transforms on active/inactive cards (no more width mismatch with navbar)
- Remove blue border/outline on active card by not setting selected/elevated attributes
- Active card now uses class-based highlighting with proper padding
- Enter key directly opens active card URL inline instead of calling click()
- Pages open in a full-viewport webview overlay instead of a new window
- Escape closes the browse overlay and returns to card stream
- Browse overlay includes its own peek-navbar with back/forward/reload and URL bar
- Scroll to bottom on load wrapped in requestAnimationFrame for reliable timing
- Keyboard navigation disabled during inline browse mode