fix(core): align DynamicValueSchema with resolveActionParam's runtime contract

[hata33]

Summary

DynamicValueSchema rejects shapes that resolveActionParam resolves correctly at runtime, producing false positives for tools that schema-validate emitted specs against ActionBindingSchema:

resolveActionParam({ $index: true }, ctx);                   // → 2
resolveActionParam(["a", "b"], ctx);                         // → ["a", "b"]
resolveActionParam({ id: { $state: "/form/text" } }, ctx);   // → { id: "hi" }

DynamicValueSchema.safeParse({ $index: true }).success;       // false
DynamicValueSchema.safeParse(["a", "b"]).success;             // false
DynamicValueSchema.safeParse({ id: { $state: "/x" } }).success; // false

All three shapes are documented API (the schema rules shipped in packages/react/src/schema.ts tell the model to use { "$item": "field" }`` and { "$index": true }`` inside repeated children, and the runtime recursively resolves arrays and plain-object values via resolvePropValue).

Changes

Widen the union in packages/core/src/types.ts:

• { $item: string } — resolves to an absolute state path in action params
• { $index: true } — resolves to the current repeat index
• arrays of dynamic values (recursive)
• records whose values are dynamic values (recursive), mirroring the runtime's plain-object recursion

The expression object arms stay strict, so a malformed { $state: 123 } still fails its dedicated arm — it only passes via the record arm, exactly matching the runtime, which treats it as a literal passthrough object.

Tests

Added a parity block to packages/core/src/types.test.ts that runs each widened shape through both DynamicValueSchema.safeParse and resolveActionParam, pinning schema/runtime agreement:

pnpm vitest run packages/core/src
Test Files  12 passed (12)
     Tests  511 passed (511)

Fixes #296

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