Implement chat and markdown views, enhance status bar, and add workflow panel

- Added `chat.rs` for rendering chat messages with timestamps and roles.
- Introduced `markdown.rs` for rendering markdown content with styling.
- Created `status.rs` to display the application status bar with session and message counts.
- Developed `workflow.rs` to show the current workflow status, including tool calls and active jobs.
- Established a `theme.rs` for centralized color management across the UI.
- Updated `mod.rs` to include new modules and manage rendering logic.

src/app/state/diff.rs

@@ -0,0 +1,40 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct StateDiff {
+    changes: Vec<Change>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Change {
+    pub path: String,
+    pub kind: String,
+}
+
+impl StateDiff {
+    pub fn new() -> Self {
+        StateDiff { changes: Vec::new() }
+    }
+
+    pub fn add_change(&mut self, path: String, kind: String) {
+        self.changes.push(Change { path, kind });
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.changes.is_empty()
+    }
+
+    pub fn clear(&mut self) {
+        self.changes.clear();
+    }
+}
+
+pub fn compute_diff(before: &serde_json::Value, after: &serde_json::Value) -> Vec<Change> {
+    if before == after {
+        return Vec::new();
+    }
+    vec![Change {
+        path: ".".to_string(),
+        kind: "modified".to_string(),
+    }]
+}