feat(react): add the Drawer primitive

[ivanbanov]

Summary

Adds the Drawer primitive across both scopes:

• @dunky.dev/drawer (packages/core/drawer) — the framework-free state machine carrying all behavior.
• @dunky.dev/react-drawer (packages/react/drawer) — the thin React binding, stories, and tests.

A drawer is a modal panel that slides in from a screen edge — semantically a dialog with a placement (left | right | top | bottom, default right). Placement is pure configuration: it never gates behavior and rides along as a data-placement styling hook on the visual layers next to data-state, so slide animations key off attributes. Always modal in v0 — no modal/role switch; snap points and swipe gestures are out of scope by decision.

Stacked PR: this PR is stacked on the feat/floating extraction PR and targets that branch; it will retarget to main once feat/floating merges.

Anatomy

• Drawer — root; owns the machine and the open/close contract
• Drawer.Trigger — button that toggles the drawer
• Drawer.Portal — reparents the visual layers to the document body
• Drawer.Backdrop — dimming layer behind the panel
• Drawer.Viewport — positioning surface for the panel
• Drawer.Content — the panel itself (role="dialog")
• Drawer.Title / Drawer.Description — accessible name and description
• Drawer.Close — button that closes the drawer

Behavior

• The full dialog contract: focus trap inside the panel, scroll lock while open, and dismissal via Escape and outside press — each gateable and vetoable.
• Topmost-layer-first stacking through the shared layer stack, so nested layered primitives dismiss in order.
• Controlled open contract: a controlled drawer reports every open/close intent through onOpenChange but only moves when the prop changes — ignoring a report is a working veto.
• ARIA: role="dialog", aria-modal, aria-labelledby/aria-describedby wired to Title/Description; trigger carries aria-haspopup, aria-expanded, and aria-controls.
• Styling hooks: data-state="open | closed" everywhere, plus data-placement on Backdrop, Viewport, and Content.

Test plan

• pnpm test:ci — 13 files, 162 tests passing
• pnpm typecheck
• pnpm lint
• pnpm format:check
• pnpm build

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