fix: make recording sheet adjustable with accessibility actions

[janicduplessis]

Description

The recording sheet advertised an adjustable role but ignored increment and decrement actions, so assistive-technology users could not change its detent. The grab area now maps increment to expanded and decrement to collapsed using the existing spring values and expanded state. Its current-state label continues to follow the sheet.

Closes #8

Test plan

• On the Stim-owned iOS simulator, recorded the collapsed grab area as Expand hike stats; the action list was absent and Notes was not visible.
• Verified the final grab area registers increment and decrement actions, with typed handlers that drive the existing expanded and collapsed spring targets.
• Verified tap expands and collapses the sheet, pan expands it, Notes becomes visible, and the label changes to Collapse hike stats.
• agent-device does not expose a standard adjustable-action invocation command, so action registration was verified in the rendered implementation while the shared state transitions were exercised through both touch paths.

Before

The sheet is collapsed with the Expand hike stats label and no Notes field.

After

The sheet is expanded with the Collapse hike stats label and the Notes field visible.