feat: run comparison - structured diff view

[camielvs]

Description

Sixth PR in the Compare Runs stack. Adds the Structured view — the main list-based way of reading a comparison.

It shows a summary line (how many tasks were added / removed / changed / unchanged, plus how many had a different outcome) and a Show unchanged toggle to hide the noise. Below that, inputs, tasks and outputs are listed in sections, each row showing exactly what changed:

• Per-task detail: diff status, per-run execution status (with an arrow when the outcome differs), changed arguments/annotations, cache changes, and the artifact comparison from the previous PR.
• A Compare logs button that opens a side-by-side log diff for tasks that ran in both runs and changed.
• Input/output detail rows with the same treatment.

Related Issue and Pull requests

Part of the Compare Runs stack. Builds on #2600; the next PR (#2602) 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.
• On the Structured tab, confirm:
  • The summary counts (added / removed / changed / unchanged / outcome differs) look right, and Show unchanged hides/shows unchanged rows.
  • Tasks, inputs and outputs are grouped into sections, with changed fields listed on each row.
  • A task with a different outcome is highlighted and shows both runs' statuses.
  • Compare logs opens a side-by-side log diff for a task that ran in both runs.
  • Two identical runs show a "no differences" state.

Additional Comments

[github-actions]

🎩 Preview

A preview build has been created at: cmp-06-structured-diff-view/de2ad56

[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 👈 (View in Graphite)
• feat: run comparison - run metadata comparison #2600
• feat: run comparison - artifact comparison #2599
• 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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