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/models/news.rs

@@ -0,0 +1,62 @@
+use serde::{Deserialize, Serialize};
+
+/// Categories for classifying AI news articles.
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub enum NewsCategory {
+    /// Large language model announcements and updates
+    Llm,
+    /// AI agent frameworks and tooling
+    Agents,
+    /// Data privacy and regulatory compliance
+    Privacy,
+    /// AI infrastructure and deployment
+    Infrastructure,
+    /// Open-source AI project releases
+    OpenSource,
+}
+
+impl NewsCategory {
+    /// Returns the display label for a news category.
+    pub fn label(&self) -> &'static str {
+        match self {
+            Self::Llm => "LLM",
+            Self::Agents => "Agents",
+            Self::Privacy => "Privacy",
+            Self::Infrastructure => "Infrastructure",
+            Self::OpenSource => "Open Source",
+        }
+    }
+
+    /// Returns the CSS class suffix for styling category badges.
+    pub fn css_class(&self) -> &'static str {
+        match self {
+            Self::Llm => "llm",
+            Self::Agents => "agents",
+            Self::Privacy => "privacy",
+            Self::Infrastructure => "infrastructure",
+            Self::OpenSource => "open-source",
+        }
+    }
+}
+
+/// A single news feed card representing an AI-related article.
+///
+/// # Fields
+///
+/// * `title` - Headline of the article
+/// * `source` - Publishing outlet or author
+/// * `summary` - Brief summary text
+/// * `category` - Classification category
+/// * `url` - Link to the full article
+/// * `thumbnail_url` - Optional thumbnail image URL
+/// * `published_at` - ISO 8601 date string
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub struct NewsCard {
+    pub title: String,
+    pub source: String,
+    pub summary: String,
+    pub category: NewsCategory,
+    pub url: String,
+    pub thumbnail_url: Option<String>,
+    pub published_at: String,
+}