Error page lacks title and token-based styling

Root error page needs polish.

Affected area:

• apps/web/src/routes/+error.svelte

Issues:

• No <svelte:head> title.
• Uses hardcoded #666 instead of design tokens.

Expected:

• Branded error title such as {page.status} · Issues.
• Styling uses existing CSS variables.

Acceptance criteria:

• Add route head title.
• Replace hardcoded colour with the appropriate design token.