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/components/mod.rs

@@ -1,8 +1,24 @@
 mod app_shell;
 mod card;
+mod chat_bubble;
+mod file_row;
 mod login;
+mod member_row;
+pub mod news_card;
+mod page_header;
+mod pricing_card;
 pub mod sidebar;
+pub mod sub_nav;
+mod tool_card;
 
 pub use app_shell::*;
 pub use card::*;
+pub use chat_bubble::*;
+pub use file_row::*;
 pub use login::*;
+pub use member_row::*;
+pub use news_card::*;
+pub use page_header::*;
+pub use pricing_card::*;
+pub use sub_nav::*;
+pub use tool_card::*;