Move dialogs onto Reka UI primitives

[jwahdatehagh]

Summary

• replace the handwritten native/compat dialog behavior with Reka Dialog primitives for modal focus containment, inert background behavior, Escape/outside policies, focus restoration, and accessible title/description wiring
• implement global confirmations with AlertDialog so cancellation receives safe initial focus and form nesting cannot submit accidentally
• preserve v-model:open, slots, compat, clickOutside, closable, large, fallthrough attributes, and transition-complete closed behavior
• add a shared per-target dialog stacking root that orders nested dialogs locally without overtaking the global toast z-index
• add interaction, axe, dynamic-attribute, compatibility, transition, stacking, and confirmation regressions

Compatibility

This keeps the wrapper API but intentionally changes the default surface from native <dialog> to a Reka-managed <div role="dialog">. Consumers styling dialog[open] or dialog::backdrop should use .dialog[data-state="open"] and .dialog-overlay. In compat mode, the overlay now precedes the article within .dialog-layer. The Changeset and component documentation call out these selector migrations.

Validation

• pnpm test
• pnpm typecheck
• pnpm lint
• pnpm format:check
• pnpm build
• git diff --check
• two independent review passes; all P0/P1 findings resolved

Stack

This is stacked on #102, which upgrades Reka UI to 2.10.3 and adds the component interaction/a11y harness and repository quality gates. Review this PR as the single commit after #102.

Follow-up

Concurrent useConfirm() calls still share the existing singleton contract and can supersede one another. A queue or explicit rejection policy should be designed separately rather than hidden inside this primitive migration.