Summary:

Refactors IssueSyncer to eliminate redundant metadata duplication between YAML frontmatter and markdown body, treating frontmatter as the single source of truth.

Does this PR resolve an issue? (Required)

Closes #7758

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills this requirement:

• It's submitted to the dev branch, not the main branch

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information: