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/model/mod.rs

@@ -0,0 +1,10 @@
+pub mod agent_def;
+pub mod app_config;
+pub mod conversation;
+pub mod editlog;
+pub mod memory;
+pub mod msglog;
+pub mod session;
+pub mod session_lock;
+pub mod settings;
+pub mod store;