refactor: replace valibot with minimal inline StandardSchemaV1 schemas

[psd-coder]

Overview

Removes valibot as a runtime/bundled dependency by replacing it with minimal inline schema
helpers that implement the StandardSchemaV1 protocol directly.

Problem Statement

valibot was a runtime dependency bundled into the library output, adding unnecessary weight. The
library only used a small subset of valibot's API (type coercion and basic validation) and the
StandardSchemaV1 protocol it already depends on is sufficient to implement those directly — no
third-party schema library is needed at runtime.

Solution Approach

• Replaced all valibot schema usage in builders.ts with three small helpers:
  • schema() — creates a raw StandardSchemaV1-conforming object
  • propSchema() — wraps coercion logic with fallback resolution and nullable short-circuit,
    eliminating the repeated pattern across all prop builders
  • fail() — constructs a StandardSchemaV1 issue result, deduplicating the error path across
    number, oneOf, and refSchema validators
• Moved valibot to devDependencies so it remains available for tests, where it serves as an
  example of a user-provided StandardSchemaV1-compatible schema passed to propBuilders.json()
• Updated the bundle size limit to reflect the new output (±30 B vs original)

Breaking Changes

None.

Testing

All existing tests pass.

[github-actions]

size-limit report 📦

Path	Size
.size-check/index.mjs	2.35 KB (+0.76% 🔺)
.size-check/render.mjs	410 B (0%)
.size-check/context.mjs	402 B (0%)