docs: group CALM Studio with the other tools under Working with CALM (finos#2667)

Consolidate the CALM Studio docs into the main Working with CALM section
so all CALM tools sit together, and remove the standalone CALM Studio
entry from the top navigation (it mixed user-facing and developer docs).

- Add a single, tool-focused CALM Studio page under Working with CALM
- Remove the CALM Studio top-nav item and its dedicated sidebar
- Drop the CALM Studio developer-guide and ADR pages
- Move the Architecture Discovery Skill tutorial from Advanced to
  Practitioner (the Advanced category is now empty and removed)
- Alphabetise the Working with CALM navigation and index list

Author: rocketstack-matt