Dashboard: Collapsible sections - authoring UX

[alex-fedotyev]

Summary

Follow-up to #1896 (core collapsible sections mechanics, merged as #1900). This issue covers the authoring experience and schema evolution for dashboard sections.

What was delivered (PR #1926)

Schema: DashboardSection → DashboardContainer

Introduced a polymorphic DashboardContainer abstraction with a type discriminator field ('section' for now). This future-proofs the data model for tabs and groups without requiring another migration.

• DashboardSectionSchema → DashboardContainerSchema with type: enum(['section']).default('section')
• sectionId → containerId on tiles
• sections → containers on dashboards
• Updated across all packages (common-utils, API, app)

Authoring UX

Action	How
Create section	Dashboard ... overflow menu → "Add Section"
Rename section	Click the title text directly (inline editing, Kibana pattern)
Delete section	Hover header → ... → Delete Section (tiles ungrouped, not deleted)
Collapse/expand	Click section header
Toggle default collapsed	Hover header → ... → Collapse/Expand by Default
Add tile to section	Hover section header → + button
Move tile to/from section	Hover tile → grid icon → pick section or "(Ungrouped)"

UX decisions (from Grafana/Datadog/Kibana competitor research)

• Click-to-rename instead of menu → Rename → type (fewer steps)
• Hover-only edit controls — ... menu and + hidden in view mode (clean default)
• "Add Section" in overflow menu — not equal prominence to "Add Tile" (less frequent action)
• "Move to Section" before delete — more discoverable position in tile toolbar

Follow-up work (not in scope)

These are enabled by the data model but need separate implementation:

• Drag tiles between sections — needs react-dnd custom drag layer; containerId update is the only data change
• Reorder sections — needs sortable list (@dnd-kit/sortable or similar); just reorder containers array
• Tab containers — add 'tab' to type enum, build tab bar UI
• Group containers — add 'group' to type enum, build bordered container UI

Dependencies

• Dashboard: Collapsible sections - core mechanics #1896 must be merged first ✅ (merged as feat: Collapsible dashboard sections - core mechanics #1900)