Add CSS-only nested dropdown submenu primitives

[developit]

Motivation

• Provide a lightweight way to author nested/child dropdown menus while adhering to the toolkit's CSS-first, low-JS philosophy.

Description

• Add three new submenu primitives: DropdownMenuSub, DropdownMenuSubTrigger, and DropdownMenuSubContent implemented with the existing createSimpleComponent pattern so they incur no runtime overhead.
• Extend public types (src/components/dropdown-menu/types.ts) and export the new components from the package entrypoint so consumers can use the API.
• Implement pure-CSS behavior in src/components/dropdown-menu/style.css using :hover and :focus-within to show/hide positioned child panels and support to="left" alignment for constrained layouts.
• Add a demo NestedDropdownDemo in demo/src/routes/home.tsx to exercise two-level nested menus (including a left-flipped second-level submenu) without introducing new command wiring or runtime logic.

Testing

• Ran pnpm -s build which completed successfully.
• Ran pnpm -s build && pnpm -s build:demo which completed successfully and produced a demo build.
• Executed an automated Playwright snippet to open the demo and capture a screenshot to validate nested hover/focus behavior which succeeded and produced nested-dropdown.png.
• Ran pnpm -s exec biome check on the changed files which reported formatting suggestions (formatter output) and flagged a check failure; the functional builds and demo verification remained successful.

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Codex Task

[github-actions]

Size Change: +274 B (+1.98%)

Total Size: 14.1 kB

Filename	Size	Change
dist/index.css	8.53 kB	+140 B (+1.67%)
dist/index.js	5.56 kB	+134 B (+2.47%)

_{compressed-size-action}

[developit]

@copilot resolve the merge conflicts in this pull request

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[Copilot]

@copilot resolve the merge conflicts in this pull request

Resolved. The merge conflicts with origin/main have been fixed in commit 856850e.

The main branch had refactored attribute selectors from [p="..."] to [k="..."], unified dropdown items into a shared Item component, and added installAdaptiveCommands + mobile drawer support. Key resolutions:

• dropdown-menu/index.tsx — adopted k= selectors and Item; DropdownMenuSubTrigger now uses createSimpleComponent('item', ...) so it participates in keyboard navigation with [k="item"] selectors
• dropdown-menu/style.css — updated submenu CSS to k= selectors; added @position-try --k-submenu-left fallback rule and anchor-based submenu positioning inside the @supports block
• dropdown-menu/types.ts — kept DropdownMenuSubTriggerOwnProps/DropdownMenuSubTriggerProps; item types now re-exported from ../item/types
• demo/src/routes/home.tsx — NestedDropdownDemo updated to use kinu imports and Item component
• commands.ts / popover/style.css — accepted main's versions in full

Library builds successfully (npm run build). CodeQL scan: 0 alerts.