doc: python script support

[JosiahParry]

Following ricochet PR #477 we now have Python script support. We need to document this. Some notes are

1. Requirements for Python content
   - Must have .python-version file (specifies target Python version, e.g., 3.12 or 3.12.7)
   - Must have uv.lock file (generated by uv lock)
   - .python-version must satisfy requires-python constraint in uv.lock
2. uv binary resolution
   - Vendored: $RICOCHET_HOME/vendor/py/uv (preferred)
   - Fallback: uv on system PATH
3. Python version discovery
   - Only uv-managed Python installations are used
   - Command: uv python list --only-installed --managed-python --no-python-downloads
4. uv cache location
   - $RICOCHET_HOME/.cache/uv
   - Created automatically during first Python deployment
5. Environment restoration command
   - uv sync --python <path> --cache-dir <cache> --no-python-downloads --frozen --color always
6. Content types supported
   - Python (invokable scripts)
7. Limitations
   - K8s/Docker exec-env support not yet implemented (local execution only)
   - Python versions must be pre-installed via uv

[JosiahParry]

Closed #83 in favor of a new PR