Update calm.finos.org documentation to explain calm template, docify and the available widgets

Enhance the CALM documentation site to include:

1. **Flow Concept**
- Automatically generated documentation for `flows` defined in CALM models (including transitions, participating nodes, and relationships).
- Human-readable tables and diagrams showing how data and control moves across systems.

2. **CLI Commands for Documentation**
- Generated reference pages for the CALM CLI (`calm template`, `calm docify`).
- Ensure commands, flags, usage examples, and output descriptions are consistently available on calm.finos.org.

3. **Case Studies**
- The test fixtures across the codebase now have a plethora of example architectures documented in CALM. They should be centralised under the home menu.

This will make the documentation more complete, discoverable, and user-friendly for developers, architects, and governance stakeholders.

Start at the calm.finos.org documentation site and inspect the existing home menu, CALM flow documentation, and CLI reference structure. Review the test fixtures containing example CALM architectures and the current `calm template` and `calm docify` entry points; done means flows, command flags and examples, and centralised case studies are discoverable with diagrams or tables where requested.

Written by the indexing model from the issue text.