feat: extract models from command-code dist, load via models.json

- Add scripts/extract-models.ts to parse command-code npm dist file
- Generate models.json (21 models, 15 pricing entries) with contextWindow
  and maxOutputTokens pre-filled; no nulls or hardcoded fallbacks in index.ts
- Rewrite index.ts to load model list and costs from models.json
- Cap gateway model maxOutputTokens at 65536 (API limit for Baseten/Vercel)
- Add 'Update models' section to README documenting the generation flow
- Add npm run extract-models script

package.json

@@ -21,6 +21,7 @@
   "files": [
     "index.ts",
     "src/",
+    "models.json",
     "README.md",
     "LICENSE"
   ],
@@ -34,7 +35,8 @@
     "test:abort": "tsx tests/test-abort.ts",
     "test:stream": "tsx tests/test-stream.ts",
     "test:pi-local": "node tests/test-pi-local.mjs",
-    "test:smoke": "node tests/test-smoke.mjs"
+    "test:smoke": "node tests/test-smoke.mjs",
+    "extract-models": "tsx scripts/extract-models.ts"
   },
   "pi": {
     "extensions": [