feat(ux): Sprint 3 mobile nav, sync conflicts, and resilience

Improve mobile bottom navigation, accessible dialogs and cards, explicit
sync conflict resolution, i18n error messages, encrypted draft autosave,
and persistent storage hints for offline data safety.

Co-authored-by: Cursor <cursoragent@cursor.com>

client/src/services/entryDraft.ts

@@ -0,0 +1,53 @@
+import { db } from './db.js'
+import { encryptJson, decryptJson } from './crypto.js'
+import { getActiveMasterKey } from './auth.js'
+
+export interface EntryDraftRecord {
+  logbookId: string
+  entryId: string
+  encryptedData: string
+  iv: string
+  tag: string
+  updatedAt: string
+}
+
+export async function saveEntryDraft(
+  logbookId: string,
+  entryId: string,
+  payload: unknown
+): Promise<void> {
+  const masterKey = getActiveMasterKey()
+  if (!masterKey) return
+
+  const { ciphertext, iv, tag } = await encryptJson(payload, masterKey)
+  await db.entryDrafts.put({
+    logbookId,
+    entryId,
+    encryptedData: ciphertext,
+    iv,
+    tag,
+    updatedAt: new Date().toISOString()
+  })
+}
+
+export async function loadEntryDraft<T = unknown>(
+  logbookId: string,
+  entryId: string
+): Promise<T | null> {
+  const masterKey = getActiveMasterKey()
+  if (!masterKey) return null
+
+  const row = await db.entryDrafts.get([logbookId, entryId])
+  if (!row) return null
+
+  try {
+    return (await decryptJson(row.encryptedData, row.iv, row.tag, masterKey)) as T
+  } catch {
+    await db.entryDrafts.delete([logbookId, entryId])
+    return null
+  }
+}
+
+export async function clearEntryDraft(logbookId: string, entryId: string): Promise<void> {
+  await db.entryDrafts.delete([logbookId, entryId])
+}