refactor(functions): standardize documentation, metadata, and wrappers

- Add comprehensive `--description` flags to all fish functions for better `help` and `functions` output.
- Introduce and correct `--wraps` flags to ensure proper completions for aliased commands (e.g., `top` wrapping `btop`, `zellij`, `upgrade` wrapping `paru`).
- Prepend descriptive comments before function definitions for better source readability.
- Add standard copyright and SPDX license identifiers to shell scripts.
- Enhance script robustness by ensuring consistent terminal checks (Kitty, WezTerm) and graceful fallbacks in window/tab spawning functions (`spwin`, `tab`).
- Implement graceful fallbacks to basic core utilities when preferred modern alternatives are missing (e.g., `top` falling back to system `top` if `btop` is missing, `view` falling back to `less` or `cat` if `nvim` is unavailable).
- Improve overall code consistency across the `functions/` directory.

functions/upgrade.fish

@@ -4,6 +4,6 @@
 # Function for upgrading the system with paru.
 # This runs `paru` with the `-Syu` flags to sync, refresh, and upgrade all
 # packages, and adds `--no-confirm` to bypass the confirmation prompt.
-function upgrade
+function upgrade --wraps='paru' --description 'packages, and adds `--no-confirm` to bypass the confirmation prompt.'
     paru -Syu --noconfirm
 end