feat: add last updated timestamp

[ashchen738]

Pre-flight Checklist

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• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project adheres to.

Description of Change

• Adding a timestamp to keep track of the last time checks for updates was run

Motivation and Context

• Refer to this issue

Screenshots

https://drive.google.com/file/d/1hO7g2_ZA92I5Ls5mg1CaHssa5X_VqSM-/view?usp=sharing

Checklist

• My pull request is properly named
• The changes respect the code style of the project (pnpm prepare-code)
• pnpm test passes
• I tested/previewed my changes locally

Release Notes

[Copilot]

Pull Request Overview

This PR adds a “last updated timestamp” to track the time when update checks are executed. The key changes are:

• Adding a new observable (lastUpdateCheckTime) in the app store that is initialized from settings and updated on each update check.
• Passing and displaying the last update check timestamp in the settings screens.
• Adding a new action (setLastUpdateCheckTime) to update the settings with the current timestamp.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/stores/AppStore.ts	Adds the lastUpdateCheckTime observable and updates it during the update check routine.
src/containers/settings/EditSettingsScreen.tsx	Passes the lastUpdateCheckTime property to the settings view.
src/components/settings/settings/EditSettingsForm.tsx	Displays the last update check timestamp in the UI and updates its prop interface.
src/actions/app.ts	Introduces a new action for updating the last update check timestamp.

Comments suppressed due to low confidence (1)

src/stores/AppStore.ts:564

• The debug message was changed from 'sending event' to 'ending event', which might be a typo. Please confirm whether this message accurately reflects the intended behavior.

debug('_checkForUpdates: ending event to autoUpdate:check');

[Copilot]

The prop type for lastUpdateCheckTime is defined as string, however it can be null in the AppStore. Consider updating the type to 'string | null' to more accurately reflect the possible values.