The Rust parser now treats `type:` as the canonical frontmatter field
for entity type, with `Is A:` and `is_a:` accepted as legacy aliases.
Previously it was the other way around, creating an asymmetric
read/write cycle since the frontend and all 8800+ vault notes already
use `type:`.
- Flip serde attribute: rename="type", alias="Is A", alias="is_a"
- Update theme defaults, getting-started vault, and type definitions
- Add round-trip tests for both type: and Is A: parsing
- Update mock data and TypeScript tests to use canonical form
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>