add deprecated model fallback chain resolution

models can now be marked `deprecated: true` with a `fallback` slug
pointing to a replacement. `resolveCliModel` follows the chain
recursively (with cycle detection) until it finds a non-deprecated
model. this keeps deprecated models in the registry for backward
compatibility instead of removing them.

marks opencode/mimo-v2-pro-free as deprecated with fallback to
opencode/nemotron-3-super-free.

Made-with: Cursor

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@pullfrog/pullfrog",
-  "version": "0.0.188",
+  "version": "0.0.189",
   "type": "module",
   "files": [
     "index.js",