feat(task): record and display task completion time

Add DoneAt to the download task model: set when a task finishes and
cleared when it is downloaded again. The value flows through the API
model and task record, and is shown as "Completed at" in the task
drawer info tab next to the creation time.

ui/flutter/macos/Podfile.lock

@@ -7,7 +7,8 @@ PODS:
     - FlutterMacOS
   - device_info_plus (0.0.1):
     - FlutterMacOS
-  - file_picker (0.0.1):
+  - file_picker_darwin (1.0.0):
+    - Flutter
     - FlutterMacOS
   - flutter_inappwebview_macos (0.0.1):
     - FlutterMacOS
@@ -41,7 +42,7 @@ DEPENDENCIES:
   - desktop_drop (from `Flutter/ephemeral/.symlinks/plugins/desktop_drop/macos`)
   - desktop_multi_window (from `Flutter/ephemeral/.symlinks/plugins/desktop_multi_window/macos`)
   - device_info_plus (from `Flutter/ephemeral/.symlinks/plugins/device_info_plus/macos`)
-  - file_picker (from `Flutter/ephemeral/.symlinks/plugins/file_picker/macos`)
+  - file_picker_darwin (from `Flutter/ephemeral/.symlinks/plugins/file_picker_darwin/darwin`)
   - flutter_inappwebview_macos (from `Flutter/ephemeral/.symlinks/plugins/flutter_inappwebview_macos/macos`)
   - flutter_local_notifications (from `Flutter/ephemeral/.symlinks/plugins/flutter_local_notifications/macos`)
   - FlutterMacOS (from `Flutter/ephemeral`)
@@ -68,8 +69,8 @@ EXTERNAL SOURCES:
     :path: Flutter/ephemeral/.symlinks/plugins/desktop_multi_window/macos
   device_info_plus:
     :path: Flutter/ephemeral/.symlinks/plugins/device_info_plus/macos
-  file_picker:
-    :path: Flutter/ephemeral/.symlinks/plugins/file_picker/macos
+  file_picker_darwin:
+    :path: Flutter/ephemeral/.symlinks/plugins/file_picker_darwin/darwin
   flutter_inappwebview_macos:
     :path: Flutter/ephemeral/.symlinks/plugins/flutter_inappwebview_macos/macos
   flutter_local_notifications:
@@ -96,25 +97,25 @@ EXTERNAL SOURCES:
     :path: Flutter/ephemeral/.symlinks/plugins/window_manager/macos
 
 SPEC CHECKSUMS:
-  app_links: 05a6ec2341985eb05e9f97dc63f5837c39895c3f
-  desktop_drop: e0b672a7d84c0a6cbc378595e82cdb15f2970a43
-  desktop_multi_window: 93667594ccc4b88d91a97972fd3b1b89667fa80a
-  device_info_plus: 4fb280989f669696856f8b129e4a5e3cd6c48f76
-  file_picker: 7584aae6fa07a041af2b36a2655122d42f578c1a
-  flutter_inappwebview_macos: c2d68649f9f8f1831bfcd98d73fd6256366d9d1d
-  flutter_local_notifications: 4bf37a31afde695b56091b4ae3e4d9c7a7e6cda0
+  app_links: c3185399a5cabc2e610ee5ad52fb7269b84ff869
+  desktop_drop: 69eeff437544aa619c8db7f4481b3a65f7696898
+  desktop_multi_window: 566489c048b501134f9d7fb6a2354c60a9126486
+  device_info_plus: 1b14eed9bf95428983aed283a8d51cce3d8c4215
+  file_picker_darwin: 27e043831d68462d54f1c40e724b1f53c9d1e8be
+  flutter_inappwebview_macos: bdf207b8f4ebd58e86ae06cd96b147de99a67c9b
+  flutter_local_notifications: 14e285ca39907db50704f7f46c9ab7a526bd7ead
   FlutterMacOS: d0db08ddef1a9af05a5ec4b724367152bb0500b1
-  open_dir_macos: 79810d7921d777f8732bf6358b3a0839a8fad9b5
+  open_dir_macos: 9649018f88e71eb9fb8aa3d95caec30a73c08c5b
   OrderedSet: e539b66b644ff081c73a262d24ad552a69be3a94
-  package_info_plus: f0052d280d17aa382b932f399edf32507174e870
-  screen_retriever_macos: c5508cc3c66ff0d4db650480cf0ab691e220d933
-  share_plus: 510bf0af1a42cd602274b4629920c9649c52f4cc
-  shared_preferences_foundation: 7036424c3d8ec98dfe75ff1667cb0cd531ec82bb
-  tray_manager: a104b5c81b578d83f3c3d0f40a997c8b10810166
-  uri_content: 5f98ff12ded3f2e1681b689828d747bafb03ba5f
-  url_launcher_macos: f87a979182d112f911de6820aefddaf56ee9fbfd
-  window_manager: b729e31d38fb04905235df9ea896128991cad99e
+  package_info_plus: 12f1c5c2cfe8727ca46cbd0b26677728972d9a5b
+  screen_retriever_macos: 038d3f7b34a779b06f536842003e41e8ec1fb4b7
+  share_plus: 1fa619de8392a4398bfaf176d441853922614e89
+  shared_preferences_foundation: 5086985c1d43c5ba4d5e69a4e8083a389e2909e6
+  tray_manager: c2a678ee19e2a094f0c2d03660ee2c3e81cea8ab
+  uri_content: e002074bcf6fbf905a3909603f9a2b1b490fce67
+  url_launcher_macos: 175a54c831f4375a6cf895875f716ee5af3888ce
+  window_manager: e25faf20d88283a0d46e7b1a759d07261ca27575
 
 PODFILE CHECKSUM: 54d867c82ac51cbd61b565781b9fada492027009
 
-COCOAPODS: 1.17.0
+COCOAPODS: 1.15.2