Add built-in theme support with various pre-defined themes

- Introduce multiple built-in themes (`default_dark`, `default_light`, `gruvbox`, `dracula`, `solarized`, `midnight-ocean`, `rose-pine`, `monokai`, `material-dark`, `material-light`).
- Implement theming system with customizable color schemes for all UI components in the TUI.
- Include documentation for themes in `themes/README.md`.
- Add fallback mechanisms for default themes in case of parsing errors.
- Support custom themes with overrides via configuration.

README.md

@@ -3,13 +3,13 @@
 > Terminal-native assistant for running local language models with a comfortable TUI.
 
 ![Status](https://img.shields.io/badge/status-alpha-yellow)
-![Version](https://img.shields.io/badge/version-0.1.8-blue)
+![Version](https://img.shields.io/badge/version-0.1.9-blue)
 ![Rust](https://img.shields.io/badge/made_with-Rust-ffc832?logo=rust&logoColor=white)
 ![License](https://img.shields.io/badge/license-AGPL--3.0-blue)
 
 ## Alpha Status
 
-- This project is currently in **alpha** (v0.1.8) and under active development.
+- This project is currently in **alpha** (v0.1.9) and under active development.
 - Core features are functional but expect occasional bugs and missing polish.
 - Breaking changes may occur between releases as we refine the API.
 - Feedback, bug reports, and contributions are very welcome!
@@ -48,6 +48,7 @@ The OWLEN interface features a clean, multi-panel layout with vim-inspired navig
 - **Session Management** - Start new conversations, clear history, browse saved sessions
 - **Thinking Mode Support** - Dedicated panel for extended reasoning content
 - **Bracketed Paste** - Safe paste handling for multi-line content
+- **Theming System** - 10 built-in themes plus custom theme support
 
 ### Code Client (`owlen-code`) [Experimental]
 - All chat client features
@@ -140,14 +141,17 @@ cargo build --release --bin owlen-code --features code-client
 - `Enter` - Send message and return to normal mode
 - `Ctrl-J` / `Shift-Enter` - Insert newline
 - `Ctrl-↑/↓` - Navigate input history
+- `Ctrl-A` / `Ctrl-E` - Jump to start/end of line
+- `Ctrl-W` / `Ctrl-B` - Word movement
+- `Ctrl-R` - Redo
 - Paste events handled automatically
 
 **Visual Mode**:
 - `j/k/h/l` - Extend selection
 - `w/b/e` - Word-based selection
 - `y` - Yank (copy) selection
-- `d` - Cut selection (Input panel only)
-- `Esc` - Cancel selection
+- `d` / `Delete` - Cut selection (Input panel only)
+- `Esc` / `v` - Cancel selection
 
 **Command Mode**:
 - `Tab` - Autocomplete selected command suggestion
@@ -160,8 +164,17 @@ cargo build --release --bin owlen-code --features code-client
 - `:save [name]` / `:w [name]` - Save current conversation
 - `:load` / `:open` - Browse and load saved sessions
 - `:sessions` / `:ls` - List saved sessions
+- `:theme <name>` - Switch theme (saved to config)
+- `:themes` - Browse themes in interactive modal
+- `:reload` - Reload configuration and themes
 - *Commands show real-time suggestions as you type*
 
+**Theme Browser** (accessed via `:themes`):
+- `j` / `k` / `↑` / `↓` - Navigate themes
+- `Enter` - Apply selected theme
+- `g` / `G` - Jump to top/bottom
+- `Esc` / `q` - Close browser
+
 **Session Browser** (accessed via `:load` or `:sessions`):
 - `j` / `k` / `↑` / `↓` - Navigate sessions
 - `Enter` - Load selected session
@@ -210,15 +223,63 @@ generate_descriptions = true  # AI-generated summaries for saved sessions
 
 Configuration is automatically saved when you change models or providers.
 
+### Theming
+
+OWLEN includes 10 built-in themes that are embedded in the binary. You can also create custom themes.
+
+**Built-in themes:**
+- `default_dark` (default) - High-contrast dark theme
+- `default_light` - Clean light theme
+- `gruvbox` - Retro warm color scheme
+- `dracula` - Vibrant purple and cyan
+- `solarized` - Precision colors for readability
+- `midnight-ocean` - Deep blue oceanic theme
+- `rose-pine` - Soho vibes with muted pastels
+- `monokai` - Classic code editor theme
+- `material-dark` - Google's Material Design dark variant
+- `material-light` - Google's Material Design light variant
+
+**Commands:**
+- `:theme <name>` - Switch theme instantly (automatically saved to config)
+- `:themes` - Browse and select themes in an interactive modal
+- `:reload` - Reload configuration and themes
+
+**Setting default theme:**
+```toml
+[ui]
+theme = "gruvbox"  # or any built-in/custom theme name
+```
+
+**Creating custom themes:**
+
+Create a `.toml` file in `~/.config/owlen/themes/`:
+
+```toml
+# ~/.config/owlen/themes/my-theme.toml
+name = "my-theme"
+text = "#ffffff"
+background = "#000000"
+focused_panel_border = "#ff00ff"
+unfocused_panel_border = "#800080"
+user_message_role = "#00ffff"
+assistant_message_role = "#ffff00"
+# ... see themes/README.md for full schema
+```
+
+**Colors** can be hex RGB (`#rrggbb`) or named colors (`red`, `blue`, `lightgreen`, etc.). See `themes/README.md` for the complete list of supported color names.
+
+For reference theme files and detailed documentation, see the `themes/` directory in the repository or `/usr/share/owlen/themes/` after installation.
+
 ## Repository Layout
 
 ```
 owlen/
 ├── crates/
-│   ├── owlen-core/       # Core types, session management, shared UI components
+│   ├── owlen-core/       # Core types, session management, theming, shared UI components
 │   ├── owlen-ollama/     # Ollama provider implementation
 │   ├── owlen-tui/        # TUI components (chat_app, code_app, rendering)
 │   └── owlen-cli/        # Binary entry points (owlen, owlen-code)
+├── themes/               # Built-in theme definitions (embedded in binary)
 ├── LICENSE               # AGPL-3.0 License
 ├── Cargo.toml            # Workspace configuration
 └── README.md
@@ -270,9 +331,9 @@ cargo fmt
 - [x] Bracketed paste support
 - [x] Command autocompletion with Tab completion
 - [x] Session persistence (save/load conversations)
+- [x] Theming system with 9 built-in themes and custom theme support
 
 ### In Progress
-- [ ] Theming options and color customization
 - [ ] Enhanced configuration UX (in-app settings)
 - [ ] Conversation export (Markdown, JSON, plain text)
 
@@ -322,4 +383,4 @@ Built with:
 
 ---
 
-**Status**: Alpha v0.1.8 | **License**: AGPL-3.0 | **Made with Rust** 🦀
+**Status**: Alpha v0.1.9 | **License**: AGPL-3.0 | **Made with Rust** 🦀