CI and Notification Enhancements

[sadeeq6400]

This pull request addresses several key areas of the application, including push notifications, CI stability, test coverage, and application startup.

• Task 1: [Enhancement] Push notification token registration is stubbed with three TODOs and never reaches a backend
  Implemented real token registration and de-registration endpoints.
  Synchronized notification preferences with the backend.
  Handled token refresh when Expo rotates the push token.
  Added a NOTIFICATION_STRATEGY.md document to define the contract with the backend.
  Closes [Enhancement] Push notification token registration is stubbed with three TODOs and never reaches a backend #1004

• Task 2: [Enhancement] Add a CI job that fails when the test suite executes zero tests
  Added a new CI job that fails when the test suite executes zero tests.
  Configured Jest to output a JSON report for analysis.
  Closes [Enhancement] Add a CI job that fails when the test suite executes zero tests #1005

Task 3: [Enhancement] Publish and enforce test coverage thresholds
Added a coverageThreshold to jest.config.js to enforce minimum coverage levels.
Set global and per-directory thresholds for critical paths.
Added a coverage-reporting step to the CI workflow.
Closes #1006

Task 4: [Enhancement] Add an integration test for the cold-start sequence
Added an integration test that boots the real entry point and asserts each initialization step ran, in order.
Added a performance-budget.json file to assert startup duration against a budget.
Closes #1007

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