[codex] Add repeatable manifest node contract

[artiphishle]

What changed

• added a generic UiNodeRepeatSpec contract with source, itemAlias, and keyPath
• extended UiNode with optional repeat support
• added a serialization test covering a repeated container, item-context prop bindings, and generic navigate event bindings
• added a patch changeset for @ankhorage/contracts

Why

Issue 06 needs a manifest-level primitive for repeated child rendering so starter templates can bind live collections without introducing product- or scanner-specific contract types.

Impact

• contracts can now describe repeated direct-child rendering from existing binding sources
• repeated item context can stay generic via context.<itemAlias>.*
• existing dataBindings.events semantics remain unchanged

Validation

• bun test src/bindings.test.ts src/contracts.test.ts
• bun run lint:fix