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/utils/noteListHelpers.test.ts

@@ -0,0 +1,82 @@
+import { describe, it, expect, vi, afterEach } from 'vitest'
+import { formatSubtitle, relativeDate } from './noteListHelpers'
+import type { VaultEntry } from '../types'
+
+function makeEntry(overrides: Partial<VaultEntry> = {}): VaultEntry {
+  return {
+    path: '/vault/note/test.md', filename: 'test.md', title: 'Test',
+    isA: 'Note', aliases: [], belongsTo: [], relatedTo: [],
+    status: null, owner: null, cadence: null, archived: false,
+    trashed: false, trashedAt: null,
+    modifiedAt: null, createdAt: null, fileSize: 0,
+    snippet: '', wordCount: 0, relationships: {},
+    icon: null, color: null, order: null, outgoingLinks: [],
+    ...overrides,
+  }
+}
+
+describe('formatSubtitle', () => {
+  afterEach(() => { vi.restoreAllMocks() })
+
+  it('shows date and word count when both available', () => {
+    const entry = makeEntry({ modifiedAt: 1700000000, wordCount: 342 })
+    const result = formatSubtitle(entry)
+    expect(result).toContain('342 words')
+    expect(result).toContain('\u00b7')
+  })
+
+  it('shows "Empty" when word count is 0', () => {
+    const entry = makeEntry({ modifiedAt: 1700000000, wordCount: 0 })
+    const result = formatSubtitle(entry)
+    expect(result).toContain('Empty')
+    expect(result).not.toContain('words')
+  })
+
+  it('shows only word count when no date available', () => {
+    const entry = makeEntry({ wordCount: 100 })
+    expect(formatSubtitle(entry)).toBe('100 words')
+  })
+
+  it('shows only "Empty" when no date and no content', () => {
+    const entry = makeEntry()
+    expect(formatSubtitle(entry)).toBe('Empty')
+  })
+
+  it('falls back to createdAt when modifiedAt is null', () => {
+    const entry = makeEntry({ createdAt: 1700000000, wordCount: 50 })
+    const result = formatSubtitle(entry)
+    expect(result).toContain('50 words')
+    expect(result).toContain('\u00b7')
+  })
+})
+
+describe('relativeDate', () => {
+  it('returns empty string for null', () => {
+    expect(relativeDate(null)).toBe('')
+  })
+
+  it('returns "just now" for recent timestamps', () => {
+    const now = Math.floor(Date.now() / 1000)
+    expect(relativeDate(now)).toBe('just now')
+  })
+
+  it('returns minutes ago for timestamps within an hour', () => {
+    const fiveMinAgo = Math.floor(Date.now() / 1000) - 300
+    expect(relativeDate(fiveMinAgo)).toBe('5m ago')
+  })
+
+  it('returns hours ago for timestamps within a day', () => {
+    const twoHoursAgo = Math.floor(Date.now() / 1000) - 7200
+    expect(relativeDate(twoHoursAgo)).toBe('2h ago')
+  })
+
+  it('returns days ago for timestamps within a week', () => {
+    const threeDaysAgo = Math.floor(Date.now() / 1000) - 86400 * 3
+    expect(relativeDate(threeDaysAgo)).toBe('3d ago')
+  })
+
+  it('returns formatted date for older timestamps', () => {
+    // Use a fixed timestamp: Nov 14, 2023
+    expect(relativeDate(1700000000)).toMatch(/Nov 14/)
+  })
+})