fix: sync deletion propagation, add base64 util, timeout, and merge improvements

Critical:
- Add deleted column: deleteMeasurement now soft-deletes, merge filters
  out deleted items based on updatedAt (was: deletions were resurrected)
- Replace btoa with UTF-8-safe encodeBase64 utility for Hermes compat

Important:
- Preserve createdAt when overwriting duplicate-date measurements
- Add 15s AbortController timeout to all WebDAV fetch calls
- Revert broken date prefilling regression (MeasurementForm)
- getAllMeasurements/latest/byDate now filter deleted records
- Replace Dimensions with useWindowDimensions for rotation awareness
- Replace silent catch with console.warn in HistoryScreen

Tests: 8 new tests for deletion merge cases and soft-delete queries

tests/database.test.ts

@@ -19,6 +19,7 @@ const mockMeasurement: Measurement = {
   createdAt: '2024-01-01T08:00:00.000Z',
   updatedAt: '2024-01-01T08:00:00.000Z',
   syncStatus: 'local',
+  deleted: 0,
 }
 
 describe('database', () => {
@@ -28,6 +29,8 @@ describe('database', () => {
   let getAllMeasurements: any
   let getLatestMeasurement: any
   let updateMeasurement: any
+  let deleteMeasurement: any
+  let getAllMeasurementsIncludingDeleted: any
 
   beforeEach(async () => {
     jest.resetModules()
@@ -35,8 +38,8 @@ describe('database', () => {
       openDatabaseAsync: jest.fn(),
     }))
     db = {
-      execAsync: jest.fn(),
-      runAsync: jest.fn(),
+      execAsync: jest.fn(() => Promise.resolve()),
+      runAsync: jest.fn(() => Promise.resolve()),
       getAllAsync: jest.fn(),
     }
     const sqlite = require('expo-sqlite')
@@ -47,6 +50,8 @@ describe('database', () => {
     getAllMeasurements = mod.getAllMeasurements
     getLatestMeasurement = mod.getLatestMeasurement
     updateMeasurement = mod.updateMeasurement
+    deleteMeasurement = mod.deleteMeasurement
+    getAllMeasurementsIncludingDeleted = mod.getAllMeasurementsIncludingDeleted
   })
 
   it('initDatabase creates the measurements table', async () => {
@@ -91,4 +96,33 @@ describe('database', () => {
       expect.arrayContaining(['synced', mockMeasurement.id])
     )
   })
+
+  it('deleteMeasurement marks measurement as deleted', async () => {
+    db.runAsync.mockResolvedValue(undefined)
+    await initDatabase()
+    await deleteMeasurement(mockMeasurement.id)
+    expect(db.runAsync).toHaveBeenCalledWith(
+      expect.stringContaining('UPDATE measurements SET deleted = 1'),
+      expect.arrayContaining([mockMeasurement.id])
+    )
+  })
+
+  it('getAllMeasurements filters out deleted records', async () => {
+    await initDatabase()
+    await getAllMeasurements()
+    expect(db.getAllAsync).toHaveBeenCalledWith(
+      expect.stringContaining('deleted = 0')
+    )
+  })
+
+  it('getAllMeasurementsIncludingDeleted includes deleted records', async () => {
+    await initDatabase()
+    await getAllMeasurementsIncludingDeleted()
+    expect(db.getAllAsync).toHaveBeenCalledWith(
+      expect.stringContaining('SELECT * FROM measurements')
+    )
+    expect(db.getAllAsync).not.toHaveBeenCalledWith(
+      expect.stringContaining('deleted = 0')
+    )
+  })
 })