feat(platform/react): Base44ChatProvider, reading hooks and parts

[amitbardos]

Stacked on base44/javascript-sdk#315 (the hook). Supersedes base44/javascript-sdk#314, which was written against the hook's earlier contract. Design and alternatives: Partner chat: provider design.

What

The drawing layer above useBase44Chat. It adds nothing below the hook's contract.

<Base44ChatProvider appId={appId} backend={backend} onAppCreated={selectApp}
  components={{ question: { Choice, Secrets, Approval } }}>
  <Messages />   {/* useChatState().items, each drawn with <Message item={item} /> */}
  <Composer />   {/* useChatState().status, useChatActions().send */}
</Base44ChatProvider>

• <Base44ChatProvider> runs the hook once and shares it through context.
• Two reading hooks. useChatState() returns items, status, connection and error, and re-renders on every event. useChatActions() returns send, create and clearError, and keeps its identity while the app stays the same, also with an inline backend or onAppCreated.
• Question parts are required. TypeScript refuses components.question without Choice, Secrets and Approval. A release that adds a kind adds a part, so the upgrade names it; until then the hook declines the kind.
• Message parts are optional. Text and Step fall back to plain HTML with a data-base44 attribute and no classes.
• <Message> draws the text, then each step followed by its open question. It adds no element of its own. <Question> draws a question anywhere below the provider.
• Message, Question and the reading hooks throw a clear error outside a provider.

Packaging

TSX support in tsconfig, the type tests, vitest and eslint. Every new module starts with "use client", which the package test asserts.

Tests

• tests/unit/react/provider.test.tsx: draw order, each part answering its own tool call, replaced parts, pending prompts, <Question> elsewhere, errors outside a provider, re-render and identity stability with inline props.
• tests/types/react-provider.types.tsx: required question parts, no Unknown, bound actions per kind.
• tests/package.test.mjs: the new exports resolve from the tarball, and the declarations compile under NodeNext, Bundler and Node.

npm test -w @base44/platform and lint pass locally.

Not in this PR

The Tiny Sunny example (examples/react-chat) from #314. It follows once the design doc settles whether to ship message primitives.

🤖 Generated with Claude Code

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