feat(site): wrap behavior page sections in CollapsibleSection cards - #23991

🤖 This PR was written by Coder Agent on behalf of Danielle Maywood 🤖

PR 2/4 in a stack to unify agent settings pages.

What

Wraps all Behavior page sections in CollapsibleSection cards and cleans up the compaction settings component.

Why

The settings pages currently use flat <hr> dividers between sections, which makes it hard to visually group related controls. Wrapping each section in a collapsible bordered card gives clearer visual boundaries and lets users collapse sections they are not actively editing. This is the same pattern the Spend page (PR 4) uses, so applying it to Behavior first establishes consistency across the settings area.

Changes

AgentSettingsBehaviorPageView — each section (Instructions, Context Compaction, System Instructions, Virtual Desktop, Workspace Autostop, Kyleosophy) wrapped in <CollapsibleSection>. Admin sections show AdminBadge in the badge slot and toggle switches in the action slot. The AdminBadge component has a built-in ml-auto class that would push it to the right inside the CollapsibleSection header — the badge slot wraps it with [&>*]:ml-0 to neutralize this.

UserCompactionThresholdSettings — gains a hideHeader prop so the CollapsibleSection card can provide the header instead. The header block (title + description) was previously duplicated 3 times across loading/error/success branches; now hoisted to a single const headerBlock at the top of the component. Cancel/Save buttons moved out of TableFooter into a standalone <div className="flex justify-end gap-2 pt-2"> — Save is always visible (disabled when dirtyRows.length === 0) so users can see the action exists without needing to make edits first.

Stories — updated 3 play functions that referenced the renamed section title ("Personal Instructions" → "Instructions"), and 3 UserCompactionThresholdSettings assertions that expected the Save button to be absent when no rows are dirty (it is now always rendered but disabled).

Stack

1. CollapsibleSection + shared fixes (feat(site): add CollapsibleSection component and shared utilities #23990)
2. ➡️ This PR — Behavior page CollapsibleSection cards
3. Analytics DateRangePicker (feat(site): add DateRangePicker to analytics page #23992)
4. Unified Spend page (feat: merge Limits + Usage into unified Spend page #24093)