feat: generate cdk.json JSON Schema from cli-config source of truth

[9pace]

Adds a generated JSON Schema for `cdk.json` as a 4th output target in `user-input-gen`, alongside the existing yargs, types, and config conversion outputs. Because it's generated from `cli-config.ts`, it can never drift from actual supported options.

What's included:

• Schema generator covering all global options + per-command config blocks
• Warn-only validation on config load (recurses into command namespaces, never blocks)
• `$schema` pointer injected by `cdk init` for IDE autocomplete
• Schema included in npm package

Design decisions:

• Generated, not hand-written (PR feat: manually generated json-schema with validation #919 covered ~25 of 150+ properties manually)
• `additionalProperties: true` at root (custom keys allowed), `false` on command blocks (typo detection)
• No external validator dependency (lightweight recursive type checking)

Checklist

• This change contains a major version upgrade for a dependency and I confirm all breaking changes are addressed

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[codecov-commenter]

Codecov Report

❌ Patch coverage is 48.64865% with 57 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.76%. Comparing base (2c4acf7) to head (8bb64a5).

Files with missing lines	Patch %	Lines
packages/aws-cdk/lib/cli/validate-config.ts	35.95%	57 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1573      +/-   ##
==========================================
- Coverage   88.16%   87.76%   -0.41%     
==========================================
  Files          76       77       +1     
  Lines       10841    10952     +111     
  Branches     1494     1510      +16     
==========================================
+ Hits         9558     9612      +54     
- Misses       1255     1312      +57     
  Partials       28       28              

Flag	Coverage Δ
suite.unit	87.76% <48.64%> (-0.41%)	⬇️

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[github-actions]

Total lines changed 1605 is greater than 1000. Please consider breaking this PR down.