feat: replace 'Is a' / 'is_a' with 'type' as the canonical frontmatter key

- Rust Frontmatter struct now parses both 'type' (new) and 'Is A'/'is_a' (legacy),
  with 'type' taking precedence via resolve_type()
- Added migrate_is_a_to_type() vault-wide migration (runs on startup, also exposed as Tauri command)
- Frontend: buildNoteContent and resolveNewType now emit 'type:' in YAML
- Inspector SKIP_KEYS hides 'is_a', 'Is A', 'type', 'title' from property list
  (TypeRow already renders the type with its dedicated UI)
- frontmatterToEntryPatch handles both 'type' and legacy 'is_a' keys
- Mock data updated: all YAML content uses 'type:' instead of 'is_a:'/'Is A:'
- Tests updated to expect 'type:' in generated frontmatter

Product decision: internal VaultEntry field stays as `isA` (TS) / `is_a` (Rust)
to minimize blast radius. The user-facing change is the YAML key and inspector.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/DynamicPropertiesPanel.tsx

@@ -27,8 +27,8 @@ export const RELATIONSHIP_KEYS = new Set([
   'Advances', 'Parent', 'Children', 'Has', 'Notes',
 ])
 
-// Keys to skip showing in Properties
-const SKIP_KEYS = new Set(['aliases', 'notion_id', 'workspace', 'is_a', 'Is A'])
+// Keys to skip showing in Properties (handled by dedicated UI or internal)
+const SKIP_KEYS = new Set(['aliases', 'notion_id', 'workspace', 'title', 'type', 'is_a', 'Is A'])
 
 // eslint-disable-next-line react-refresh/only-export-components -- utility co-located with component
 export function containsWikilinks(value: FrontmatterValue): boolean {