feat: copy anchor on every heading

[barredterra]

No description provided.

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge with no actionable correctness or security failures identified.

Heading identifiers and labels are escaped before DOM insertion, copied fragments are encoded and decoded consistently, and the new behavior is covered by an integration test.

_{Reviews (1): Last reviewed commit: "feat: copy anchor on every heading" | Re-trigger Greptile}