Yu Yan taking over: complete server date protection for timelog and weekly summary

[yany960]

Description

This PR takes over and replaces the abandoned work from PR #4312 to fully protect timelog and weekly summary flows from local/system date manipulation.

Related PRs

• Replaces frontend PR: Yu Yan taking over for Durga venkata praveen resolved server date issue frontend #4312
• Related backend PR: Yu Yan taking over for Durga venkata praveen resolved server date issue backend HGNRest#1875
• Original related frontend reference from notes: Koushica - Fix changing system date will allow user to log time on a different date #3335

Main changes explained

• Added ServerTimeContext to centralize authoritative server-date access and periodic re-sync logic.
• Wrapped the app in ServerTimeProvider so time-sensitive flows can use the same server-based date source.
• Added GET_SERVER_DATE frontend endpoint wiring for the related backend API.
• Updated TimeEntryForm to initialize and refresh dateOfWork from server time instead of the local machine clock.
• Updated TimeEntry same-day checks to use server time rather than local time.
• Updated Timelog week boundary calculations and date labels to use server time.
• Updated WeeklySummary due-date initialization and week-belonging checks so the dashboard due date no longer follows modified local/system time.
• Updated affected unit tests to render through ServerTimeProvider.

Why this replaces PR #4312

Review feedback on #4312 showed that changing the computer date/time could still:

• Shift the weekly summary due date on the dashboard
• Change the default date used in time entry flows
• Allow users to log time into the wrong week

This replacement PR keeps the original server-date approach but closes the remaining gaps where local moment() usage was still leaking into weekly summary and timelog behavior.

How to test

1. Check out codex/yuyan-pr4312-server-date.
2. Run the related backend from PR Shiwani old badges unit test #1875.
3. Start the frontend locally.
4. Change your computer date/time to a different week or month.
5. Verify the time-entry date still reflects server time.
6. Verify the weekly summary due date still reflects server time.
7. Verify the behavior in both light mode and dark mode.

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[sonarqubecloud]

Quality Gate passed

Issues
6 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
2.4% Duplication on New Code

See analysis details on SonarQube Cloud