feat: diagnose unresolved template state references

[fzdwx]

A generated selection summary used a JavaScript conditional inside $template. The renderer treated the entire interpolation as a state path and displayed an empty value, while validateSpec reported no issue.

Add opt-in checkTemplateStateRefs validation for absolute template paths. References must resolve in initial state or be covered by a declared binding or literal action write path. Diagnostics include the exact JSON Pointer, including inactive conditional branches and action parameters. The default remains disabled; rendering and expression resolution are unchanged. Literal keys containing operator characters remain valid, and bare repeat-item names are left alone.

Validation:

• 40 core spec-validator tests passed, including the captured failure pattern and valid literal/future-write/binding references.
• Core tsconfig.check.json passed.
• Matching v0.21.0 ESM, CJS and declaration build passed for the downstream consumer.
• Downstream system Chrome verified the diagnostic and repair payload, then selection and reversible pressed icon feedback in App and a frozen offline file.
• Full workspace pnpm type-check was attempted but could not start because Turbo/workspace dependencies are not installed in the isolated checkout.

[vercel]

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