Show joined issue cards in incident activity

[arseniycodes]

Summary

• render the triggering and joined issues through one shared activity-card presentation
• replace legacy joined-issue UUID/error summaries with concise timeline labels while preserving timestamp and order
• support existing context-change events whose issue ID appears only in the legacy summary

Why

Joined issues were rendered as raw lifecycle copy because older context-change events did not carry a structured issue ID. That made incident activity difficult to scan and omitted the linked error tile.

Validation

• focused incident activity and outcome tests
• web typecheck
• full web test suite (149 tests)

---

Summary by cubic

Show joined issue cards in the incident activity timeline using a shared issue card UI. We parse legacy joined-issue summaries to extract the issue ID, render a compact label, and keep timestamp and ordering.

• New Features
  • Add issue_activity items for joined issues and render them via renderIssueCard with concise labels; transcripts exclude these items.
  • Parse legacy incident_context_changed summaries to get issueId when missing from event detail; unify UI by using IssueActivityEntry (accented for the triggering issue, supports occurrences).

^{Written for commit 3ffa0be. Summary will update on new commits.}