feat(ui): add public landing page with impressum and privacy pages

Introduce a marketing landing page at `/` with hero section, feature grid,
how-it-works steps, CTA banner, and footer. Move the authenticated dashboard
to `/dashboard`. Add static Impressum and Privacy Policy pages for EU legal
compliance. Update login redirect defaults accordingly.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/pages/mod.rs

@@ -1,2 +1,9 @@
+mod impressum;
+mod landing;
 mod overview;
+mod privacy;
+
+pub use impressum::*;
+pub use landing::*;
 pub use overview::*;
+pub use privacy::*;