feat: thunar & papirus-folders theming + new schemes (#80)

* feat: GTK app theming system

- Implemented custom.css import for user-managed app themes
- process_app_themes() to dynamically update colors in imported CSS files
- Inline comment markers for color replacement (e.g, /* accent-color */)
- Papirus icon color syncing with weighted hue/saturation algorithm

This allows users to create modular app themes that automatically update when the scheme/wallpaper changes

Example usage:
  .app .element { color: #24BD5C; /* accent-color */ }
  .app .element:hover { background: rgba(36, 189, 92, 0.15); /* accent-color with 15% opacity */ }

* feat: atomic theme changes with locking and mode-specific CSS

- Implemented locking to prevent concurrent theme changes
- Added mode-light/mode-dark CSS markers for dynamic property reordering
- Made terminal writes and Papirus sync non-blocking to prevent hangs
- Only save scheme.json after successful theme application

Fixes race conditions during rapid theme switching and ensures Shell and GTK apps scheme stay in sync.

* theme: added to color mapping for custom theming, new schemes

* theme: quick fixes, cleanup

* theme: include thunar.css as template, with new theming system

* theme: modified GTK theming approach

- Dropped comment targeted theming in favor for existing {{  }} replacement
- [app].css.template file created for customization, bypassing built in default if present
- Handling *.template for added templates to be parsed and added to import

* theme: fixes for  thunar.css

* theme: remove .template file use

* theme: path button color adjustment, non-active hover

* fixes & cleanup

* thunar css fixes

* more css fixes

* format

* fix tab vert spacing

---------

Co-authored-by: 2 * r + 2 * t <61896496+soramanew@users.noreply.github.com>

README.md

@@ -18,6 +18,32 @@ The main control script for the Caelestia dotfiles.
 
 </details>
 
+<details><summary id="optional-dependencies">Optional dependencies</summary>
+
+-   [`papirus-folders`](https://github.com/PapirusDevelopmentTeam/papirus-folders) - automatic folder icon color syncing with theme
+
+> [!NOTE]
+> For automatic Papirus folder icon color syncing, `papirus-folders` needs to be able to run with `sudo` without a password prompt.
+> 
+> **Recommended** - Create a sudoers file:
+> ```fish
+> # Fish shell
+> echo "$USER ALL=(ALL) NOPASSWD: "(which papirus-folders) | sudo tee /etc/sudoers.d/papirus-folders
+> sudo chmod 440 /etc/sudoers.d/papirus-folders
+> ```
+> ```sh
+> # Bash/other shells
+> echo "$USER ALL=(ALL) NOPASSWD: $(which papirus-folders)" | sudo tee /etc/sudoers.d/papirus-folders
+> sudo chmod 440 /etc/sudoers.d/papirus-folders
+> ```
+> 
+> **Alternatively** - Edit the main sudoers file by running `sudo visudo` and adding at the end:
+> ```
+> your_username ALL=(ALL) NOPASSWD: /usr/bin/papirus-folders
+> ```
+
+</details>
+
 ## Installation
 
 ### Arch linux