Expand theme support and add color customization options

The plugin currently uses Obsidian's theme variables for styling, which works well with most themes. However, adding more customization options would allow users to fine-tune the appearance.

**Proposed Changes:**
- Add color picker settings for each token type (commands, functions, keywords, etc.)
- Provide preset color themes based on popular editor themes (Dracula, Nord, Solarized, etc.)
- Support light/dark theme detection with appropriate defaults
- Add background color and text decoration options
- Test compatibility with more Obsidian themes
- Document color customization in the settings panel

**Benefits:**
- Better visual integration with users' preferred Obsidian themes
- Improved accessibility through customizable contrast
- Consistency with other language plugins in Obsidian
- Better visual hierarchy and code readability

**Related Code:**
Color settings would be added to `DQLSyntaxSettings` interface in `src/main.ts` and applied via `styles.css`.