feat: run comparison - artifact comparison

[camielvs]

Description

Fourth PR in the Compare Runs stack. Adds artifact comparison — the ability to see how a task's output artifacts differ between the two runs.

For each output artifact it shows whether it was added, removed, changed or unchanged. Small inline values are shown directly side by side; larger artifacts show their type and size, with a Compare button that opens a full-screen dialog previewing both runs' versions next to each other (reusing the existing artifact preview components). Artifacts that are too large or can't be previewed are handled gracefully.

Not wired into a page yet — the later task diff view consumes this.

Related Issue and Pull requests

Part of the Compare Runs stack. Builds on #2598; the next PR (#2600) builds on this branch.

Type of Change

• New feature

Checklist

• I have tested this does not break current pipelines / runs functionality
• I have tested the changes on staging

Screenshots (if applicable)

Test Instructions

Reachable once the stack is wired up (#2603).

• Check out the top of the stack, enable the Compare runs beta flag, and compare two runs that both produced output artifacts on the same task.
• Expand a task and confirm:
  • Artifacts show the correct Added / Removed / Changed / Unchanged status.
  • Small inline values are shown side by side for both runs.
  • Larger/previewable artifacts show a Compare button that opens the dialog with both runs' previews.
  • Non-previewable or oversized artifacts show a sensible message instead of erroring.

Additional Comments

[camielvs]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat: run comparison - compare page, run selection & routing #2603 : 2 dependent PRs (#2604 , #2641 )
• feat: run comparison - run picker & switcher #2634
• feat: run comparison - graph diff view #2602
• feat: run comparison - structured diff view #2601
• feat: run comparison - run metadata comparison #2600
• feat: run comparison - artifact comparison #2599 👈 (View in Graphite)
• feat: run comparison - shared diff UI primitives #2598
• feat: run comparison - merged graph & change summary logic #2597
• feat: run comparison - pipeline diff engine #2596
• master

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[github-actions]

🎩 Preview

A preview build has been created at: cmp-04-artifact-comparison/d39ca43