[B2] Qualify @openelement/ui as real v0.44 dogfood

[SisyphusZheng]

Required work

Qualify @openelement/ui as real v0.44 dogfood: platform primitives first, OE compiled Elements, OE signals, Community Context Protocol, Zag where behavioral state machines are justified, Open Props for design tokens where appropriate. Do NOT use Context to reinvent CSS inheritance. Qualify representative complex primitives: dialog, dropdown/menu, tabs, inputs/forms, focus management, keyboard interactions, ARIA, state, open/light/closed boundaries, SSR/DSD, claim, reconnect/dispose.

Acceptance

The listed primitives work on the real compiled framework with observable evidence. UI is evidence, not a component-count race.

Part of umbrella #1155. Depends on: Beta.1 GO.

[SisyphusZheng]

Closed by PR #1298 (squash-merged to dev as f034a552). UI dogfood qualification delivered as CI-gated observable evidence: new fixture packages/adapter-vite/__fixtures__/ui-dogfood/ consuming @openelement/ui through the real compiled v0.44 path (packageIslands, no shims), 25 tests × 3 engines (75 pass) via new CI gate fixture:ui-dogfood:gate (ci+release tiers). Coverage matrix: dialog (top-layer/focus-trap/Escape/return-focus/:state), dropdown popover (toggle/anchor/light-dismiss/return-focus), tabs (ARIA roles/states, roving tabindex, arrow/Home/End), forms (FormData participation, constraint validation, reset/disabled), focus/keyboard/ARIA/state across all, open/light/closed boundaries incl. no-JS pass, SSR/DSD markup, claim (node-identity across hydration), reconnect/dispose. Dogfood found and fixed 5 REAL defects (RED→GREEN proven): open-dialog top-layer exit + close-echo, open-dialog :state() application, open-dropdown cross-shadow focus return, open-input irreversible fieldset-disabled, and framework renderDsd dropping delegatesFocus (SSR/CSR parity). Gap explicitly deferred to Beta.3: full ARIA menu arrow-key pattern (open-dropdown is a popover, not a menu primitive) + per-component breadth. Beta.3 follow-ups recorded in the PR body.