docs: add Vercel AI SDK structured-output integration example

[rlippmann]

Summary

Adds a Vercel AI SDK structured-output integration example showing compiler state driving host-side Zod schema selection.

Also bumps the package version from 0.7.0 to 0.7.1.

Why

This demonstrates a host behavior change that is distinct from prompt reinjection:

compiler state
  -> host selects schema
  -> structured generation request

The example keeps Context Compiler responsible for deterministic state and keeps schema selection as host-owned integration behavior.

Scope checklist

• Diff is minimal and scoped to the requested behavior
• Python/spec parity is preserved (or mismatch is explicitly documented)
• Fixture semantics are respected (exact string vs non-empty null rule)
• No unrelated refactors
• Relevant validation was run (npm test for behavior changes, or docs-only/no-runtime-change)

Notes

Validation details:

• npm run build: passed
• npm test: passed (18 files, 178 tests, 1 skipped)
• Targeted integration test: passed (2 passed, 1 skipped)
• Compiled integration example: ran successfully and offered only python_script
• If not run, why: n/a