feat(pds-landing): migrate to SvelteKit app consuming @ewanc26/pds-landing
- Add full SvelteKit app scaffolding (routes, layout, CSS, tsconfig, etc.)
- Import PDSPage from @ewanc26/pds-landing v2.0.0 with production props
- Add +layout.ts with prerender = true for adapter-static compatibility
- Update Caddy static file matcher to SvelteKit output paths (/_app/*)
- Remove stale packages.pds-landing re-export from flake.nix