feat: isolate sticky comments by job ID to prevent workflow conflicts

[TosinAF]

Summary

When multiple workflows use use_sticky_comment: true on the same PR, they previously could co-opt each other's comments due to loose bot ID/name matching. This change uses github.job to automatically isolate each workflow's sticky comment.

Problem: PR #780 added bot_name for isolation, but the fallback matching logic still had issues where comments from other workflows could be co-opted.

Solution: Use the GitHub Actions job ID (github.job) as an automatic, unique identifier for each workflow's sticky comment.

Changes

• Add hidden header <!-- sticky-job: {jobId} --> to sticky comments
• Match comments strictly by this job ID header instead of bot ID/name
• Each workflow job automatically gets its own isolated comment
• Zero configuration needed - works automatically

How It Works

# .github/workflows/claude-docs-review.yml
jobs:
  claude-docs-review:  # <-- This job ID becomes the sticky comment identifier
    steps:
      - uses: anthropics/claude-code-action@main
        with:
          use_sticky_comment: true
          # No bot_name needed! Uses job ID automatically

# .github/workflows/claude-security-review.yml
jobs:
  claude-security-review:  # <-- Different job ID = different comment
    steps:
      - uses: anthropics/claude-code-action@main
        with:
          use_sticky_comment: true

Mental Model

• One job = one sticky comment
• Same job ID = same comment gets updated (intended)
• Different job IDs = separate comments (no conflicts)

Test Plan

• [ ] Run bun test to verify new tests pass
• [ ] Run bun run typecheck to verify types
• [ ] Manual test: Create PR with two workflows using use_sticky_comment: true and verify they get separate comments
• [ ] Manual test: Re-run same workflow and verify it updates the same comment

Closes #419 Related to #780

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