docs: Added documentation on cli shell autocompletion integration.

docs/09-tools/04-shell-completion.md

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+# Command line completion
+
+As a `serverpod` user, you can enable command line completion in most shells. The Serverpod CLI supports completion through [Carapace](https://carapace.sh/), which provides tab-completion for commands, options, and their values in bash, zsh, fish, PowerShell, and more.
+
+## Installing completion
+
+### Prerequisites
+
+Install [Carapace](https://carapace.sh/) for your platform:
+
+**macOS:**
+
+```bash
+brew install carapace
+```
+
+**Ubuntu/Debian:**
+
+```bash
+sudo apt install carapace-bin
+```
+
+**Windows:**
+
+```powershell
+winget install carapace
+```
+
+For other platforms, see the [Carapace installation guide](https://carapace-sh.github.io/carapace-bin/install.html).
+
+### Enable Carapace completion for Serverpod
+
+#### Bash
+
+Install the completion spec:
+
+```bash
+serverpod completion install --tool carapace
+```
+
+Then add the following to your `~/.bashrc` to enable Carapace:
+
+```bash
+source <(carapace _carapace)
+```
+
+Restart your shell or run `source ~/.bashrc` to apply.
+
+#### Zsh
+
+Install the completion spec:
+
+```bash
+serverpod completion install --tool carapace
+```
+
+Then add the following to your `~/.zshrc` to enable Carapace:
+
+```bash
+zstyle ':completion:*' format $'\e[2;37mCompleting %d\e[m'
+source <(carapace _carapace)
+```
+
+Restart your shell or run `source ~/.zshrc` to apply.
+
+#### Other shells
+
+Carapace supports fish, PowerShell, elvish, and more. After installing the completion spec with `serverpod completion install --tool carapace`, see the [Carapace setup documentation](https://carapace-sh.github.io/carapace-bin/setup.html) for instructions specific to your shell.
+
+## Alternative: Completely
+
+The Serverpod CLI also supports [Completely](https://github.com/bashly-framework/completely), a lightweight alternative to Carapace that supports bash and zsh. Unlike Carapace, Completely does not require a separate tool running in your shell — it generates a standalone bash completion script.
+
+To generate a Completely spec and create a completion script:
+
+```bash
+serverpod completion generate --tool completely -f serverpod.yaml
+completely generate serverpod.yaml serverpod.bash
+```
+
+Then source the generated script in your shell config (e.g., `source /path/to/serverpod.bash` in `~/.bashrc` or `~/.zshrc`).
+
+:::note
+Carapace is the recommended tool as it supports a wider range of shells and comes with a pre-built completion spec that can be installed directly with `serverpod completion install`. Completely requires generating and processing the script manually.
+:::