feat(ui): add dashboard sections with sidebar navigation and mock views

Add seven sidebar sections (Dashboard, Providers, Chat, Tools,
Knowledge Base, Developer, Organization) with fully rendered mock views,
nested sub-shells for Developer and Organization, and SearXNG container
for future news feed integration. Replaces the previous OverviewPage
with a news feed dashboard.

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

src/pages/mod.rs

@@ -1,9 +1,21 @@
+mod chat;
+mod dashboard;
+pub mod developer;
 mod impressum;
+mod knowledge;
 mod landing;
-mod overview;
+pub mod organization;
 mod privacy;
+mod providers;
+mod tools;
 
+pub use chat::*;
+pub use dashboard::*;
+pub use developer::*;
 pub use impressum::*;
+pub use knowledge::*;
 pub use landing::*;
-pub use overview::*;
+pub use organization::*;
 pub use privacy::*;
+pub use providers::*;
+pub use tools::*;