feat!: replace zellij with tuios, default to ghostty + kitty (#349)

* feat!: replace zellij with tuios and switch to ghostty + kitty

Terminal environment overhaul:

- add the tuios flake input (upstream 0.8.5; nixpkgs has 0.8.1) and link
  the checked-in config out-of-store; auto-start tuios in nushell instead
  of zellij
- remove zellij entirely: both modules, config, README and nushell
  completions
- remove foot and alacritty, which lack the Kitty graphics protocol;

home/base/core/editors/helix/README.md

@@ -19,7 +19,7 @@ multi-cursor, surround), and a smaller moving part than a large Neovim plugin st
    1. <https://docs.helix-editor.com/commands.html> — typable commands (`:` prompt).
    1. <https://docs.helix-editor.com/configuration.html> — `config.toml`, themes, remaps.
    1. <https://github.com/helix-editor/helix/wiki> — install tips, language servers, FAQ.
-1. Prefer **Zellij** for shells and panes; use **Helix** for buffers and text.
+1. Prefer **tuios** for shells and panes; use **Helix** for buffers and text.
 1. On large codebases, navigation is often **by picker** (`Space f`, symbols, workspace search) or
    **by LSP** (`g` goto mode), complementing motion-based editing.
 1. After **git** operations (`checkout`, `merge`, `pull`, `rebase`) or whenever many files changed
@@ -38,20 +38,24 @@ Run `:tutor` inside Helix, or `hx --tutor` from the shell
 
 ### Terminal related
 
-Zellij shortcuts used often (same idea as in the Neovim notes):
+tuios shortcuts used often (leader is `Ctrl + B`; same idea as in the Neovim notes):
 
-| Action                    | Zellij shortcut |
-| ------------------------- | --------------- |
-| Floating terminal         | `Ctrl + p + w`  |
-| Horizontal split terminal | `Ctrl + p + d`  |
-| Vertical split terminal   | `Ctrl + p + n`  |
+| Action            | tuios shortcut             |
+| ----------------- | -------------------------- |
+| New pane          | `n` (window mode)          |
+| Floating terminal | `Ctrl + B`, then `Alt + F` |
+| Split horizontal  | `Ctrl + B`, then `-`       |
+| Split vertical    | `Ctrl + B`, then `\`       |
+| Command palette   | `Ctrl + P`                 |
+| Launcher          | `Alt + Space`              |
+| Detach            | `Ctrl + B`, then `d`       |
 
 In Helix, `|` / `!` and variants pipe or insert shell output on selections (see **Changes**).
 
 This flake’s Helix Home Manager module keeps **almost all default keys** but adds several
-normal-mode remaps: **`Ctrl+Shift+o`** → jump backward (because Zellij uses **`Ctrl+o`** for
-Session), `Space Space` → `:reload-all`, `Space w` / `Space q` → `:w` / `:q`, `Esc` → collapse
-selection, and `$` / `0` line jumps (see `home/base/core/editors/helix/default.nix`).
+normal-mode remaps: **`Ctrl+Shift+o`** → jump backward (leaving `Ctrl+o` free for the shell),
+`Space Space` → `:reload-all`, `Space w` / `Space q` → `:w` / `:q`, `Esc` → collapse selection, and
+`$` / `0` line jumps (see `home/base/core/editors/helix/default.nix`).
 
 ### Command mode (`:`)
 
@@ -203,12 +207,12 @@ Some bindings need an **LSP** or **tree-sitter** grammar; see notes on the keyma
    1. Helix is newer; a stable plugin system is still evolving:
       <https://github.com/helix-editor/helix/pull/8675>
 1. Neovim has an integrated terminal (similar in spirit to VS Code’s).
-   1. Helix does not ship one; use Zellij / tmux / terminal features instead.
+   1. Helix does not ship one; use tuios / tmux / terminal features instead.
    1. <https://github.com/helix-editor/helix/issues/1976#issuecomment-1091074719>
    1. <https://github.com/helix-editor/helix/pull/4649>
 1. Helix has no built-in tree panel; pair with **Yazi**, ranger, or Broot and open files from there.
    1. A tree view may arrive with plugins later; many users rely on the file picker instead.
-1. Global substitution is weaker in Helix; run replacements in another pane (Zellij) or an external
+1. Global substitution is weaker in Helix; run replacements in another pane (tuios) or an external
    tool when needed.
    1. <https://github.com/helix-editor/helix/issues/196>
    1. Neovim’s `:s` with preview remains strong for interactive refactors; external tools (e.g.
@@ -216,7 +220,7 @@ Some bindings need an **LSP** or **tree-sitter** grammar; see notes on the keyma
 1. Complexity vs batteries-included tradeoffs:
    <https://github.com/helix-editor/helix/discussions/6356>
 
-Using **Helix** (and Neovim when useful) inside **Yazi** and **Zellij** keeps editing, files, and
+Using **Helix** (and Neovim when useful) inside **Yazi** and **tuios** keeps editing, files, and
 panes explicit and scriptable — different from a single IDE window, but very composable.
 
 Helix nudges you away from reproducing VS Code/JetBrains inside one process; Neovim remains there

home/base/core/editors/helix/default.nix

@@ -111,7 +111,7 @@
         "$" = "goto_line_end";
         "0" = "goto_line_start";
 
-        # Ctrl+o opens Zellij Session
+        # keep Ctrl+o free for the shell; use C-S-o for the jumplist
         "C-S-o" = "jump_backward";
       };