Resolve merge conflicts in GradingService.java by combining refactored methods with logging

[Copilot]

Description of changes

Resolved merge conflicts between PR #21's bugfix branch and main by merging both code structures: the refactored helper methods from bugfix-multiple-proactive-feedback and the detailed [GRADING-FLOW] logging statements from main.

Conflict Resolution in GradingService.java:

• Preserved refactored method structure: ensureGradingEntityExists(), hasRepositoryLink(), findAndSetRepositoryLinkIfMissing(), syncAndUpdateGrading(), updateGradingFromExternalGrading(), handleCodeSubmissionEvent(), shouldSendCodeSubmissionEvent()
• Integrated logging statements throughout all methods for debugging flow
• Maintained commit-based deduplication logic (lastProcessedCommitSha)

Note: The local bugfix-multiple-proactive-feedback branch (commit 4478eeb) contains the resolved conflicts but requires manual push due to environment constraints. Alternatively, merging this PR will update the bugfix branch with the resolution.

How has this been tested?

• automated unit test
• automated integration test
• manual, exploratory test

Merge conflict resolution verified by inspecting the combined code structure. Build verification skipped due to Java 21 requirement vs Java 17 environment.

Checklist before requesting a review

• My code is easy to understand
• My code follows the coding guidelines of this project
• My code fulfills all acceptance criteria
• The test coverage (line and branch) is reasonably high, especially on Service classes and other classes with complex logic
• I have made corresponding changes to the documentation or
  the wiki/adr
• I made no breaking changes in the database schema or if so, I will perform a database migration

Checklist for reviewer

• The code is easy to understand
• The code follows
  the coding guidelines of
  this project
• The code is tested or if not, the reason is documented or discussed
• The added and existing tests reasonably cover the code change
• The code has no breaking changes in the database schema or if so, the assignee is aware of it and
  will perform a database migration

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