feat: create highlight manager with IndexedDB storage

Implemented TDD approach for highlight persistence:
- Created IndexedDB store with 'highlights' object store
- Added indexes for syncStatus and verseId for efficient queries
- Implemented CRUD operations: add, update, get, getAll, delete
- Added query methods: getHighlightsByVerse, getPendingHighlights
- Full test coverage with fake-indexeddb mock
- Added structuredClone polyfill for test environment

Generated with [Claude Code](https://claude.com/claude-code)

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

lib/highlight-manager.ts

@@ -0,0 +1,133 @@
+import { BibleHighlight } from '@/types'
+
+const DB_NAME = 'BiblicalGuide'
+const DB_VERSION = 2 // Increment version if schema changes
+const HIGHLIGHTS_STORE = 'highlights'
+
+let db: IDBDatabase | null = null
+
+export async function initHighlightsDatabase(): Promise<IDBDatabase> {
+  if (db) return db
+
+  return new Promise((resolve, reject) => {
+    const request = indexedDB.open(DB_NAME, DB_VERSION)
+
+    request.onerror = () => reject(new Error('Failed to open IndexedDB'))
+
+    request.onsuccess = () => {
+      db = request.result
+      resolve(db)
+    }
+
+    request.onupgradeneeded = (event) => {
+      const database = (event.target as IDBOpenDBRequest).result
+
+      // Create highlights store if it doesn't exist
+      if (!database.objectStoreNames.contains(HIGHLIGHTS_STORE)) {
+        const store = database.createObjectStore(HIGHLIGHTS_STORE, { keyPath: 'id' })
+        // Index for finding highlights by syncStatus for batch operations
+        store.createIndex('syncStatus', 'syncStatus', { unique: false })
+        // Index for finding highlights by verse
+        store.createIndex('verseId', 'verseId', { unique: false })
+      }
+    }
+  })
+}
+
+export async function addHighlight(highlight: BibleHighlight): Promise<string> {
+  const db = await initHighlightsDatabase()
+  return new Promise((resolve, reject) => {
+    const tx = db.transaction(HIGHLIGHTS_STORE, 'readwrite')
+    const store = tx.objectStore(HIGHLIGHTS_STORE)
+    const request = store.add(highlight)
+
+    request.onsuccess = () => resolve(request.result as string)
+    request.onerror = () => reject(new Error('Failed to add highlight'))
+  })
+}
+
+export async function updateHighlight(highlight: BibleHighlight): Promise<void> {
+  const db = await initHighlightsDatabase()
+  return new Promise((resolve, reject) => {
+    const tx = db.transaction(HIGHLIGHTS_STORE, 'readwrite')
+    const store = tx.objectStore(HIGHLIGHTS_STORE)
+    const request = store.put(highlight)
+
+    request.onsuccess = () => resolve()
+    request.onerror = () => reject(new Error('Failed to update highlight'))
+  })
+}
+
+export async function getHighlight(id: string): Promise<BibleHighlight | null> {
+  const db = await initHighlightsDatabase()
+  return new Promise((resolve, reject) => {
+    const tx = db.transaction(HIGHLIGHTS_STORE, 'readonly')
+    const store = tx.objectStore(HIGHLIGHTS_STORE)
+    const request = store.get(id)
+
+    request.onsuccess = () => resolve(request.result || null)
+    request.onerror = () => reject(new Error('Failed to get highlight'))
+  })
+}
+
+export async function getHighlightsByVerse(verseId: string): Promise<BibleHighlight[]> {
+  const db = await initHighlightsDatabase()
+  return new Promise((resolve, reject) => {
+    const tx = db.transaction(HIGHLIGHTS_STORE, 'readonly')
+    const store = tx.objectStore(HIGHLIGHTS_STORE)
+    const index = store.index('verseId')
+    const request = index.getAll(verseId)
+
+    request.onsuccess = () => resolve(request.result || [])
+    request.onerror = () => reject(new Error('Failed to get highlights by verse'))
+  })
+}
+
+export async function getAllHighlights(): Promise<BibleHighlight[]> {
+  const db = await initHighlightsDatabase()
+  return new Promise((resolve, reject) => {
+    const tx = db.transaction(HIGHLIGHTS_STORE, 'readonly')
+    const store = tx.objectStore(HIGHLIGHTS_STORE)
+    const request = store.getAll()
+
+    request.onsuccess = () => resolve(request.result || [])
+    request.onerror = () => reject(new Error('Failed to get all highlights'))
+  })
+}
+
+export async function getPendingHighlights(): Promise<BibleHighlight[]> {
+  const db = await initHighlightsDatabase()
+  return new Promise((resolve, reject) => {
+    const tx = db.transaction(HIGHLIGHTS_STORE, 'readonly')
+    const store = tx.objectStore(HIGHLIGHTS_STORE)
+    const index = store.index('syncStatus')
+    const request = index.getAll(IDBKeyRange.only('pending'))
+
+    request.onsuccess = () => resolve(request.result || [])
+    request.onerror = () => reject(new Error('Failed to get pending highlights'))
+  })
+}
+
+export async function deleteHighlight(id: string): Promise<void> {
+  const db = await initHighlightsDatabase()
+  return new Promise((resolve, reject) => {
+    const tx = db.transaction(HIGHLIGHTS_STORE, 'readwrite')
+    const store = tx.objectStore(HIGHLIGHTS_STORE)
+    const request = store.delete(id)
+
+    request.onsuccess = () => resolve()
+    request.onerror = () => reject(new Error('Failed to delete highlight'))
+  })
+}
+
+export async function clearAllHighlights(): Promise<void> {
+  const db = await initHighlightsDatabase()
+  return new Promise((resolve, reject) => {
+    const tx = db.transaction(HIGHLIGHTS_STORE, 'readwrite')
+    const store = tx.objectStore(HIGHLIGHTS_STORE)
+    const request = store.clear()
+
+    request.onsuccess = () => resolve()
+    request.onerror = () => reject(new Error('Failed to clear highlights'))
+  })
+}