feat(zellij): add zellij plugin with aliases and completions

Add a new plugin for the zellij terminal multiplexer providing:
- 9 shorthand aliases with dynamic prefix (z or zj to avoid conflicts)
- Background completion caching using the same pattern as the gh plugin

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugins/zellij/README.md

@@ -0,0 +1,34 @@
+# zellij
+
+This plugin provides aliases and completions for [zellij](https://zellij.dev/), the terminal workspace
+(multiplexer). To use it, add `zellij` to the plugins array in your zshrc file.
+
+```zsh
+plugins=(... zellij)
+```
+
+## Dynamic prefix
+
+The default alias prefix is `z`. If `z` is already taken by another plugin (e.g., the
+[suse](https://github.com/ohmyzsh/ohmyzsh/tree/master/plugins/suse) plugin), the prefix
+automatically falls back to `zj`.
+
+## Aliases
+
+| Alias      | Command                      | Description              |
+| ---------- | ---------------------------- | ------------------------ |
+| `z`/`zj`   | `zellij`                     | Zellij command           |
+| `za`/`zja`  | `zellij attach`              | Attach to a session      |
+| `zd`/`zjd`  | `zellij delete-session`      | Delete a session         |
+| `zda`/`zjda` | `zellij delete-all-sessions` | Delete all sessions      |
+| `zk`/`zjk`  | `zellij kill-session`        | Kill a session           |
+| `zka`/`zjka` | `zellij kill-all-sessions`   | Kill all sessions        |
+| `zl`/`zjl`  | `zellij list-sessions`       | List sessions            |
+| `zr`/`zjr`  | `zellij run`                 | Run a command in a pane  |
+| `zs`/`zjs`  | `zellij -s`                  | Start a named session    |
+
+## Completions
+
+This plugin caches the zellij completion script in the background (using the same approach as
+the [gh](https://github.com/ohmyzsh/ohmyzsh/tree/master/plugins/gh) plugin). On first load the
+cache is generated; completions become available in the next shell session.