feat: add custom ollama image with ROCm 6.1 + gfx906 support

- Add ollama/Dockerfile that builds ollama from source with AMDGPU_TARGETS=gfx906
- Uses ROCm 6.1 (rocm/dev-ubuntu-22.04:6.1.2-complete) for MI50 support
- Builds llama.cpp runner with HIPBLAS for gfx906 architecture
- Updates compose.yml to build from this Dockerfile instead of pulling ollama/ollama:latest

ai/compose.yml

@@ -58,7 +58,10 @@ services:
       - ai_backend
 
   ollama:
-    image: ollama/ollama:latest
+    build:
+      context: ./ollama
+      dockerfile: Dockerfile
+    image: ollama/ollama:rocm-gfx906
     container_name: ollama
     privileged: true
     tty: true