refactor: consolidate all roles into ansible/roles/ and update ansible.cfg

- Move all roles from playbooks/roles/ to roles/
- Update roles_path in ansible.cfg
- Add cast user to common role
- Create standalone podman role
- Add semaphore role with Podman + Quadlet support

ansible/roles/ollama/templates/ollama-override.conf.j2

@@ -0,0 +1,13 @@
+# ------------------------------------------------------------------------------
+# FILE: roles/ollama/templates/ollama-override.conf.j2
+# DESCRIPTION: Systemd drop-in for the ollama service.
+#              Sets environment variables required for AMD GPU operation
+#              and configures the model storage path.
+# Managed by Ansible — do not edit manually.
+# ------------------------------------------------------------------------------
+
+[Service]
+Environment="OLLAMA_HOST={{ ollama_host }}:{{ ollama_port }}"
+Environment="OLLAMA_MODELS={{ ollama_data_dir }}"
+Environment="HSA_OVERRIDE_GFX_VERSION={{ ollama_hsa_override_gfx_version }}"
+Environment="ROCR_VISIBLE_DEVICES=0"