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/subagent/event.rs

@@ -0,0 +1,27 @@
+use serde_json::Value;
+
+#[derive(Debug, Clone)]
+pub enum SubagentEvent {
+    StepCompleted {
+        step: usize,
+        output: String,
+    },
+    StepFailed {
+        step: usize,
+        error: String,
+    },
+    Completed {
+        output: String,
+    },
+    Failed {
+        error: String,
+    },
+    ToolCall {
+        tool: String,
+        args: Value,
+    },
+    ToolResult {
+        tool: String,
+        output: String,
+    },
+}