fix(ts-sdk): export ClusterSortOption type

[realfishsam]

Summary

• Export ClusterSortOption from the TypeScript SDK models to match the Python SDK's canonical cluster sort type.
• Keep MatchedClusterSort as an alias of ClusterSortOption for existing callers.
• Add a public type-export regression test.

Fixes #1169

Test Plan

• RED: npm test --workspace=pmxtjs -- --runInBand tests/public-exports.test.ts failed with Module '../index' has no exported member 'ClusterSortOption'.
• GREEN/static: npx tsc --noEmit --skipLibCheck --moduleResolution node --target ES2020 --module commonjs sdks/typescript/pmxt/models.ts
• Local full public-exports Jest is blocked after the fix by missing generated SDK artifacts (../generated/src/index.js). Attempted npm run generate --workspace=pmxtjs, but this runner lacks java for openapi-generator.

[realfishsam]

CI note after opening this focused #1169 fix:

• The PR itself only changes sdks/typescript/pmxt/models.ts and sdks/typescript/tests/public-exports.test.ts to add/export the ClusterSortOption type alias.
• Local focused static check passed: npx tsc --noEmit --skipLibCheck --moduleResolution node --target ES2020 --module commonjs sdks/typescript/pmxt/models.ts.
• I verified the test is meaningful before the fix: npm test --workspace=pmxtjs -- --runInBand tests/public-exports.test.ts failed with Module '../index' has no exported member 'ClusterSortOption'.
• After the fix, local full public-exports Jest is blocked by missing generated SDK artifacts (../generated/src/index.js); attempting npm run generate --workspace=pmxtjs is blocked in this runner because java is not installed for openapi-generator.
• Current red generated-sync checks show broad pre-existing/unrelated generator drift (API_REFERENCE.md sourceExchange/exchange changes, client method hosted-routing diffs, etc.) rather than drift caused by this type alias. I am keeping this PR scoped instead of folding that broad generator churn into a small TS public type export fix.