feat: add icon and color fields to VaultEntry

- Add icon (string|null) and color (string|null) to VaultEntry interface
- Update Rust VaultEntry struct and frontmatter parsing to read icon/color
- Add icon/color to SKIP_KEYS so they don't appear as relationships
- Set mock data: Recipe type → cooking-pot/orange, Book type → book-open/green
- Update all test files with the new required fields

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

src/types.ts

@@ -15,6 +15,10 @@ export interface VaultEntry {
   snippet: string
   /** Generic relationship fields: any frontmatter key whose value contains wikilinks. */
   relationships: Record<string, string[]>
+  /** Phosphor icon name (kebab-case) for Type entries, e.g. "cooking-pot" */
+  icon: string | null
+  /** Accent color key for Type entries: "red" | "purple" | "blue" | "green" | "yellow" | "orange" */
+  color: string | null
 }
 
 export interface GitCommit {