feat: add session issue tracking to update_context

[JeremyDev87]

Purpose

Track all GitHub issues created during a session in context.md automatically. Prevents duplicate creation and provides a session audit trail.

Background

In the 2026-03-21 session, ~50 issues were created across multiple PLAN cycles. Without a running list, duplicates were created (#805/#815/#820) and had to be manually identified and closed later.

Changes

• apps/mcp-server/src/ — Add issuesCreated field to update_context
• docs/codingbuddy/context.md — Auto-accumulate issue numbers per session

Expected Behavior

update_context({
  mode: "ACT",
  progress: [...],
  issuesCreated: [841, 842, 843]  // NEW field
})

→ context.md accumulates:
## Session Issues
- #841 — chore(rules): add operational safety rules
- #842 — ...
- #843 — ...
Total: 3 issues this session

Acceptance Criteria

• issuesCreated field added to update_context parameters
• context.md accumulates issue list across multiple update_context calls
• Duplicate issue numbers deduplicated automatically
• Session issue count visible in context.md
• TDD: tests first