fix: Add local backend entries for chatterbox on MacOS

- Replace container-based cpu-chatterbox and metal-chatterbox entries
  with local Python backend references
- This fixes the 'run file not found' error when installing chatterbox
  on MacOS systems
- The Python backend at backend/python/chatterbox/ is now used for
  both cpu-chatterbox and metal-chatterbox backends

Fixes #8610

Author: team-coding-agent-1

backend/index.yaml

@@ -2136,9 +2136,7 @@
     nvidia-l4t-cuda-13: "cuda13-nvidia-l4t-arm64-chatterbox-development"
 - !!merge <<: *chatterbox
   name: "cpu-chatterbox"
-  uri: "quay.io/go-skynet/local-ai-backends:latest-cpu-chatterbox"
-  mirrors:
-    - localai/localai-backends:latest-cpu-chatterbox
+  uri: "./backend/python/chatterbox"
 - !!merge <<: *chatterbox
   name: "cpu-chatterbox-development"
   uri: "quay.io/go-skynet/local-ai-backends:master-cpu-chatterbox"
@@ -2156,9 +2154,7 @@
     - localai/localai-backends:master-nvidia-l4t-arm64-chatterbox
 - !!merge <<: *chatterbox
   name: "metal-chatterbox"
-  uri: "quay.io/go-skynet/local-ai-backends:latest-metal-darwin-arm64-chatterbox"
-  mirrors:
-    - localai/localai-backends:latest-metal-darwin-arm64-chatterbox
+  uri: "./backend/python/chatterbox"
 - !!merge <<: *chatterbox
   name: "metal-chatterbox-development"
   uri: "quay.io/go-skynet/local-ai-backends:master-metal-darwin-arm64-chatterbox"