Implement the approved Base Radio Group semantic slice

Goal

Implement the maintainer-approved Base Radio Group semantic checkpoint from #349 as one bounded Base family with Root, Item, and Indicator identities.

Approved contract

• Root is the sole selected-value owner, Collection provider, Focus Roving owner, and named radiogroup object.
• Item is a focusable radio, derives checked/effective-disabled state, and requests selection.
• Indicator is passive repeatable visual feedback with no value, activation, focus, form, or accessibility-control ownership.
• Empty and unmatched values are valid; structural churn never rewrites value.
• Controlled requests signal without mutating final state; uncontrolled requests update and signal once.
• Both-axis wrapped navigation, selected-or-first entry, Space selection, Enter no-op, arrows/Home/End move and select, disabled skipping.
• Form participation, public orientation/loop, Toolbar behavior, and Shadcn/Brutalist projections remain deferred.

Delivery surface

• draft P/T catalog entities and relations;
• Base implementation and exact public exports;
• executable Base tests;
• Web Component, React, and Vue projection tests;
• CLI registry entry;
• bilingual docs and demo;
• generated Agent projection.

Acceptance criteria

• Root/Item/Indicator identity, anatomy, props, exposes, events, and absence assertions match the #349 checkpoint exactly.
• Controlled/uncontrolled, duplicate, empty/unmatched, structural churn, disabled, pointer, keyboard, focus, and independent-group behavior have executable evidence.
• Indicators remain passive and create no duplicate radio object.
• No form/native input/orientation/loop/Toolbar/Shadcn/Brutalist guarantees are introduced.
• Package, CLI, docs/demo, catalog, adapters, and generated projections agree.
• Focused tests, catalog checks, type checks, and proportional full-suite verification pass.

Claiming guidance

This is an advanced implementation task. The semantic checkpoint is complete; contributors must not reopen the approved API through implementation-by-analogy.