TypeSchema: Precompute base names for profile methods

[ryukzak]

Summary

• Add NameCandidates type (candidates: string[] + recommended: string) to ProfileExtension and FieldSlice
• New module src/typeschema/core/name-candidates.ts:
  • Language-neutral candidate generation for extensions and slices
  • Multi-level collision resolution (base → qualified → discriminated)
  • assignRecommendedBaseNames() sets recommended after profile TypeSchema is built
• Remove resolveProfileMethodBaseNames, resolveNameCollisions, and 6 dead name helpers from the TS generator
• TS profile generators now consume nameCandidates.recommended directly

Before (each language must re-implement collision detection):

// In TypeScript generator (profile.ts)
const resolvedMethodNames = resolveProfileMethodBaseNames(extensions, sliceDefs);
generateExtensionMethods(w, tsIndex, flatProfile, resolvedMethodNames.extensions);
generateSliceSetters(w, sliceDefs, flatProfile, resolvedMethodNames.slices);

After (collision-free names precomputed on TypeSchema):

// In transformer.ts — once, for all languages
assignRecommendedBaseNames(profileSchema);

// In any language generator
const baseName = ext.nameCandidates.recommended;
const baseName = slice.nameCandidates.recommended;