feat: generate Zod schemas from TypeScript types using ts-to-zod library

This refactors the type generation approach to use the ts-to-zod library
for converting TypeScript types to Zod schemas, replacing the previous
manual schema generation.

Key changes:
- Add scripts/generate-schemas.ts using ts-to-zod as a library with:
  - Custom pre-processing to inject SDK-specific features (Base64 validation,
    description JSDoc tags, RELATED_TASK_META_KEY)
  - Post-processing transforms for strict() mode, discriminatedUnions, enums
  - AST-based schema post-processing with ts-morph for robust transformations
- Generate src/generated/sdk.types.ts (pre-processed TypeScript types)
- Generate src/generated/sdk.schemas.ts (Zod schemas with SDK conventions)
- Refactor src/types.ts to re-export most schemas from generated code
- Convert Request/Notification/Result from intersection to union types
  for better type narrowing in switch statements
- Add union types: McpRequest, McpNotification, McpResult for type guards
- Fix test files for union type compatibility and new schema structures
- Add comprehensive schema comparison tests

The generated schemas maintain full compatibility with the existing API
while improving type safety and reducing manual maintenance burden.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ochafik

package-lock.json

@@ -68,6 +68,7 @@
     ],
     "scripts": {
         "fetch:spec-types": "tsx scripts/fetch-spec-types.ts",
+        "generate:schemas": "tsx scripts/generate-schemas.ts && prettier --write \"src/generated/**/*\"",
         "typecheck": "tsgo --noEmit",
         "build": "npm run build:esm && npm run build:cjs",
         "build:esm": "mkdir -p dist/esm && echo '{\"type\": \"module\"}' > dist/esm/package.json && tsc -p tsconfig.prod.json",
@@ -132,6 +133,8 @@
         "eslint-plugin-n": "^17.23.1",
         "prettier": "3.6.2",
         "supertest": "^7.0.0",
+        "ts-morph": "^27.0.2",
+        "ts-to-zod": "^5.1.0",
         "tsx": "^4.16.5",
         "typescript": "^5.5.4",
         "typescript-eslint": "^8.48.1",