feat: PWA offline capture — IndexedDB queue, service worker cache, auto-sync on reconnect

lib/offline/db.ts

@@ -1,7 +1,7 @@
-// Stub — full implementation in Task 5 (IndexedDB offline queue)
-// This file exists so TypeScript can resolve the dynamic import in report-form.tsx.
+import { openDB, type IDBPDatabase } from 'idb'
 
 export interface PendingReport {
+  id?: number
   zone_token: string
   incident_type: string
   description: string
@@ -11,6 +11,35 @@ export interface PendingReport {
   created_at: string
 }
 
-export async function addPendingReport(_report: PendingReport): Promise<void> {
-  throw new Error('IndexedDB offline store not yet implemented — Task 5 will replace this stub')
+let dbPromise: Promise<IDBPDatabase> | null = null
+
+function getDb(): Promise<IDBPDatabase> {
+  if (!dbPromise) {
+    dbPromise = openDB('ims-offline', 1, {
+      upgrade(db) {
+        db.createObjectStore('pending_reports', { keyPath: 'id', autoIncrement: true })
+      },
+    })
+  }
+  return dbPromise
+}
+
+export async function addPendingReport(report: Omit<PendingReport, 'id'>): Promise<number> {
+  const db = await getDb()
+  return db.add('pending_reports', report) as Promise<number>
+}
+
+export async function getPendingReports(): Promise<PendingReport[]> {
+  const db = await getDb()
+  return db.getAll('pending_reports')
+}
+
+export async function removePendingReport(id: number): Promise<void> {
+  const db = await getDb()
+  return db.delete('pending_reports', id)
+}
+
+export async function getPendingCount(): Promise<number> {
+  const db = await getDb()
+  return db.count('pending_reports')
 }