Remove tracked dist artifacts, drop legacy TS tests/sources, and fix AJV import for tsc

[GsCommand]

Motivation

• Remove generated dist/ artifacts from source control so build outputs are not tracked and future PRs remain clean.
• Eliminate legacy files causing TypeScript compile/test drift and remove superseded test/source files.
• Fix a TypeScript constructability error when dynamically importing ajv so npm run build and tsc succeed.

Description

• Stopped tracking dist/ and added dist/ to .gitignore so distribution files are no longer included in the repo.
• Deleted legacy files src/receipt-v1.ts and src/test/runtime-core.test.ts which were superseded by the modern sources and tests.
• Updated src/schema-client.ts to cast the dynamically imported ajv default export to a constructor (AjvCtor) and instantiate it via new AjvCtor(...) to resolve the TS constructability error.
• Did not add any src/shims.d.ts and left src/canonicalize.ts present as required.

Testing

• Ran npm install which failed in this environment due to a registry 403 Forbidden error when fetching @types/node, so full install of dev/test deps did not complete.
• Ran npm run build which succeeded after the ajv import/instantiation fix, resolving the earlier TS error.
• Ran npm test which failed due to missing test runtime helper tsx/esm (transitively unavailable because npm install did not complete).
• Ran npm run typecheck (tsc --noEmit) which passed with the applied changes.

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Codex Task