Add comprehensive documentation and examples for Owlen architecture and usage

- Include detailed architecture overview in `docs/architecture.md`.
- Add `docs/configuration.md`, detailing configuration file structure and settings.
- Provide a step-by-step provider implementation guide in `docs/provider-implementation.md`.
- Add frequently asked questions (FAQ) document in `docs/faq.md`.
- Create `docs/migration-guide.md` for future breaking changes and version upgrades.
- Introduce new examples in `examples/` showcasing basic chat, custom providers, and theming.
- Add a changelog (`CHANGELOG.md`) for tracking significant changes.
- Provide contribution guidelines (`CONTRIBUTING.md`) and a Code of Conduct (`CODE_OF_CONDUCT.md`).

examples/custom_theme.rs

@@ -0,0 +1,28 @@
+// This example demonstrates how to create a custom theme programmatically.
+
+use owlen_core::theme::Theme;
+use ratatui::style::{Color, Style};
+
+fn create_custom_theme() -> Theme {
+    Theme {
+        name: "My Custom Theme".to_string(),
+        author: "Your Name".to_string(),
+        comment: "A simple custom theme".to_string(),
+        base: Style::default().fg(Color::White).bg(Color::Black),
+        user_chat: Style::default().fg(Color::Green),
+        bot_chat: Style::default().fg(Color::Cyan),
+        error: Style::default().fg(Color::Red),
+        info: Style::default().fg(Color::Yellow),
+        border: Style::default().fg(Color::Gray),
+        input: Style::default().fg(Color::White),
+        ..Default::default()
+    }
+}
+
+fn main() {
+    let custom_theme = create_custom_theme();
+
+    println!("Created custom theme: {}", custom_theme.name);
+    println!("Author: {}", custom_theme.author);
+    println!("User chat color: {:?}", custom_theme.user_chat.fg);
+}