Move branch-slug to @getpaseo/protocol

The app must not import @getpaseo/server. Moving the slug validation
and slugify helpers into @getpaseo/protocol (already a shared dep of
app, client, server) gives every package a legitimate home for the
import. Drops the corresponding ./utils/branch-slug subpath from
@getpaseo/server's exports map.

Unblocks the Deploy App workflow, which only builds protocol/client/
audio for the app — server's dist never exists in that pipeline.

packages/server/package.json

@@ -22,11 +22,6 @@
       "types": "./dist/server/utils/tool-call-parsers.d.ts",
       "source": "./src/utils/tool-call-parsers.ts",
       "default": "./dist/server/utils/tool-call-parsers.js"
-    },
-    "./utils/branch-slug": {
-      "types": "./dist/server/utils/branch-slug.d.ts",
-      "source": "./src/utils/branch-slug.ts",
-      "default": "./dist/server/utils/branch-slug.js"
     }
   },
   "publishConfig": {