refactor(web): centralize thread details section layout

[juliusmarminge]

Retained in the V2 UI stack. The thread detail, automation, and relationship panels migrated here are absent from main.

Workspace, Version Control, Automations, and Lineage each built their own thread-details section header. Their heights and horizontal insets had drifted, and none consistently owned title truncation.

Add ThreadDetailsSection and use it for all four sections. It owns the divider, content inset, single-line nonselectable heading, and action alignment. Consumers provide the title, actions, and content. Both the sidebar and popover use it; the existing scroll container and control behavior stay intact.

Validation: the three focused thread-details/lineage tests passed, including agent status updates and disclosure behavior. Web typecheck and changed-file lint passed. React Doctor found only existing warnings in the changed web files.

No server, contracts, persisted data, or migration changes. Browser verification and before/after captures were explicitly excluded from this code-only pass. Kept as a draft pending visual review.

Model: GPT-6. Harness: Codex.

[github-actions]

Thread transfer impact

⚠️ The latest CI run did not produce a thread transfer result for 0f6aa4e.

This comment will update automatically after the next completed run.

[macroscopeapp]

Approvability

Verdict: Approved at 0f6aa4e

Macroscope's review found this PR approvable — This PR centralizes existing thread-details section markup and makes only localized spacing and header-layout adjustments. Existing data flows, conditions, accessibility labels, and interactive behavior remain unchanged, with no sensitive, schema, deployment, default, or lint-configuration impact.

No code changes detected at e929da5. Prior analysis still applies.

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