feat: note subtitle — show metadata (date + word count) (#94)

* feat: show metadata subtitle (date + word count) instead of snippet

Replace the note list subtitle with a compact metadata summary showing
relative date and word count (e.g. "2d ago · 342 words") instead of
the first paragraph of note content. Adds word_count to VaultEntry on
the Rust backend, computed during vault scan.

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

* fix: cargo fmt formatting

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/types.ts

@@ -16,6 +16,7 @@ export interface VaultEntry {
   createdAt: number | null
   fileSize: number
   snippet: string
+  wordCount: number
   /** 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" */