docs(vscode): README remove status paragraph, add theme setting; Extension rename to CALM

[markscott-ms]

Description

This pull request updates the documentation for the CALM Visual Studio Code Extension by removing the outdated status note and adding information about supported visualization themes for the live preview diagrams.

It also renames the visual name of the plugin from CALM Preview & Tools to CALM.

Current	Now
	CALM Preview & Tools is just "CALM"

Documentation updates:

• Removed the "Status" section from the top of the README.md, which previously described the extension's transition out of experimental status.
• Added a new section detailing the four supported visualization themes for live preview diagrams and how to configure the calm.docify.theme setting.

This PR affects the information seen on https://marketplace.visualstudio.com/items?itemName=FINOS.calm-vscode-plugin

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📚 Documentation update
• 🎨 Code style/formatting changes
• ♻️ Refactoring (no functional changes)
• ⚡ Performance improvements
• ✅ Test additions or updates
• 🔧 Chore (maintenance, dependencies, CI, etc.)

Affected Components

• CLI (cli/)
• Shared (shared/)
• CALM Widgets (calm-widgets/)
• CALM Hub (calm-hub/)
• CALM Hub UI (calm-hub-ui/)
• Documentation (docs/)
• VS Code Extension (calm-plugins/vscode/)
• Dependencies
• CI/CD

Commit Message Format ✅

Testing

• I have tested my changes locally
• I have added/updated unit tests
• All existing tests pass

Checklist

• My commits follow the conventional commit format
• I have updated documentation if necessary
• I have added tests for my changes (if applicable)
• My changes follow the project's coding standards