feat: add Inbox sidebar section showing unlinked notes

Inbox shows notes without valid outgoing relationships (body wikilinks
or frontmatter refs), helping users find captured but unorganized notes.
Includes time-period filter pills (This week/month/quarter/All time),
Cmd+K command, and macOS menu bar entry. Broken wikilinks (targeting
non-existent notes) are not counted as relationships.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/utils/noteListHelpers.ts

@@ -1,4 +1,4 @@
-import type { VaultEntry, SidebarSelection } from '../types'
+import type { VaultEntry, SidebarSelection, InboxPeriod } from '../types'
 
 export type NoteListFilter = 'open' | 'archived' | 'trashed'
 
@@ -353,3 +353,88 @@ export function countByFilter(entries: VaultEntry[], type: string): Record<NoteL
   }
   return { open, archived, trashed }
 }
+
+// --- Inbox ---
+
+/** Build a set of all valid link targets (titles, aliases, filename stems, path stems). */
+export function buildValidLinkTargets(entries: VaultEntry[]): Set<string> {
+  const targets = new Set<string>()
+  for (const e of entries) {
+    targets.add(e.title)
+    const fileStem = e.filename.replace(/\.md$/, '')
+    targets.add(fileStem)
+    // path stem: everything after vault root, minus .md
+    // E.g. /Users/luca/Laputa/project/foo.md → project/foo
+    const parts = e.path.replace(/\.md$/, '').split('/')
+    // Try from index that gives "folder/name" pattern — skip first segments
+    if (parts.length >= 2) {
+      const last2 = parts.slice(-2).join('/')
+      if (last2 !== fileStem) targets.add(last2)
+    }
+    for (const alias of e.aliases) targets.add(alias)
+  }
+  return targets
+}
+
+function extractRef(raw: string): string {
+  return raw.replace(/^\[\[/, '').replace(/\]\]$/, '').split('|')[0]
+}
+
+function hasValidRef(refs: string[], validTargets: Set<string>): boolean {
+  return refs.some((raw) => {
+    const inner = extractRef(raw)
+    return validTargets.has(inner) || validTargets.has(inner.split('/').pop() ?? '')
+  })
+}
+
+/** Check if entry has any valid outgoing link (body or frontmatter) that resolves to a real note. */
+export function isInboxEntry(entry: VaultEntry, validTargets: Set<string>): boolean {
+  if (entry.trashed || entry.archived) return false
+  if (entry.isA === 'Type') return false
+
+  // Check body outgoing links
+  if (entry.outgoingLinks.some((link) => validTargets.has(link) || validTargets.has(link.split('/').pop() ?? ''))) return false
+
+  // Check frontmatter relationship refs
+  if (entry.belongsTo?.length && hasValidRef(entry.belongsTo, validTargets)) return false
+  if (entry.relatedTo?.length && hasValidRef(entry.relatedTo, validTargets)) return false
+  if (entry.relationships) {
+    for (const refs of Object.values(entry.relationships)) {
+      if (hasValidRef(refs, validTargets)) return false
+    }
+  }
+
+  return true
+}
+
+const INBOX_PERIOD_DAYS: Record<InboxPeriod, number> = {
+  week: 7, month: 30, quarter: 90, all: Infinity,
+}
+
+/** Filter entries for the Inbox view: no valid relationships, within the given time period, sorted by createdAt desc. */
+export function filterInboxEntries(entries: VaultEntry[], period: InboxPeriod): VaultEntry[] {
+  const validTargets = buildValidLinkTargets(entries)
+  const now = Math.floor(Date.now() / 1000)
+  const cutoff = period === 'all' ? 0 : now - INBOX_PERIOD_DAYS[period] * 86400
+
+  return entries
+    .filter((e) => isInboxEntry(e, validTargets) && (e.createdAt ?? 0) >= cutoff)
+    .sort((a, b) => (b.createdAt ?? 0) - (a.createdAt ?? 0))
+}
+
+/** Count inbox entries per period. */
+export function countInboxByPeriod(entries: VaultEntry[]): Record<InboxPeriod, number> {
+  const validTargets = buildValidLinkTargets(entries)
+  const inbox = entries.filter((e) => isInboxEntry(e, validTargets))
+  const now = Math.floor(Date.now() / 1000)
+
+  let week = 0, month = 0, quarter = 0
+  for (const e of inbox) {
+    const age = now - (e.createdAt ?? 0)
+    if (age <= 7 * 86400) week++
+    if (age <= 30 * 86400) month++
+    if (age <= 90 * 86400) quarter++
+  }
+
+  return { week, month, quarter, all: inbox.length }
+}