feat: Add poller and case list to desktop client

This commit introduces a new poller to the desktop client, responsible
for fetching case markers and their one-liners. It also integrates a
case list UI, allowing users to view and interact with their cases.

Key changes include:

- **New Dependencies**: Added `doctate-client-core`, `time`, and
  `webbrowser` to `Cargo.lock`.
- **Background Task Spawning**: Refactored `spawn_uploader` to
  `spawn_background` to include the new `OnelinerPoller` and its
  dependencies.
- **Case Store Integration**: The `DoctateApp` now initializes and uses
  a `CaseStore` to manage case markers.
- **UI Enhancements**:
    - A new `render_case_list` function displays recent cases with their
      last activity time and one-liner.
    - Buttons to "Continue" recording for a case and "Open" the case in
      a web browser are added.
    - A staleness indicator for the poller's connection is displayed.
- **State Management**:
    - The `AppState` is updated to reflect the new UI elements and
      interactions.
    - Actions like `Continue` and `OpenWeb` are handled.
- **Configuration**: Poll interval and window hours are now configurable
  and used by the poller.
- **Error Handling**: Improved error handling for saving configuration
  and background task operations.
- **Code Cleanup**: Minor refactoring and documentation updates.

Cargo.lock

@@ -1177,6 +1177,7 @@ name = "doctate-desktop"
 version = "0.1.0"
 dependencies = [
  "directories",
+ "doctate-client-core",
  "doctate-common",
  "eframe",
  "libc",
@@ -1185,11 +1186,13 @@ dependencies = [
  "serde_json",
  "tempfile",
  "thiserror 1.0.69",
+ "time",
  "tokio",
  "toml",
  "tracing",
  "tracing-subscriber",
  "uuid",
+ "webbrowser",
  "which",
  "wiremock",
 ]