docs(installation): document the 'py' (Python) script type (#3640)

* docs(installation): document the 'py' (Python) script type

The installation guide's "Specify Script Type" section only showed
`--script sh` and `--script ps`, and the installed-variant list only
mentioned `.specify/scripts/bash/` and `.specify/scripts/powershell/`.
The CLI has a third script type, `py`: `SCRIPT_TYPE_CHOICES` in
`_agent_config.py` includes `"py": "Python"`, and `shared_infra.py`
installs a `python/` variant directory (plus the platform shell fallback)
when `--script py` is chosen.

Add the missing `--script py` force example and a `.specify/scripts/python/`
bullet so the docs match the code. Docs-only.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* docs(installation): frame Python as a first-class third script type

Address review feedback: update the section heading and intro so Python
is presented as a first-class script type alongside Shell and PowerShell,
matching the added --script py example and python/ variant directory.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: jawwad-ali

docs/installation.md

@@ -77,9 +77,9 @@ specify init <project_name> --integration pi
 specify init <project_name> --integration omp
 ```
 
-### Specify Script Type (Shell vs PowerShell)
+### Specify Script Type (Shell, PowerShell, or Python)
 
-All automation scripts now have both Bash (`.sh`) and PowerShell (`.ps1`) variants.
+Automation scripts are available as Bash (`.sh`), PowerShell (`.ps1`), and Python (`.py`) variants.
 
 Auto behavior:
 
@@ -92,6 +92,7 @@ Force a specific script type:
 ```bash
 specify init <project_name> --script sh
 specify init <project_name> --script ps
+specify init <project_name> --script py
 ```
 
 ### Ignore Agent Tools Check
@@ -131,6 +132,7 @@ Scripts are installed into a variant subdirectory matching the chosen script typ
 
 - `.specify/scripts/bash/` — contains `.sh` scripts (default on Linux/macOS)
 - `.specify/scripts/powershell/` — contains `.ps1` scripts (default on Windows)
+- `.specify/scripts/python/` — contains `.py` scripts (chosen with `--script py`; also installs the platform shell fallback)
 
 ## Troubleshooting