Add images container env var, remove image_agent

Add AZURE_STORAGE_IMAGES_CONTAINER environment variable to the MCP container app in both AVM and Bicep infrastructure definitions. Remove the unused src/backend/agents/image_agent.py.

Author: Fr4nc3

infra/avm/main.bicep

@@ -1341,6 +1341,10 @@ module containerAppMcp './modules/compute/container-app.bicep' = {
             name: 'AZURE_STORAGE_BLOB_URL'
             value: storage_account.outputs.blobEndpoint
           }
+          {
+            name: 'AZURE_STORAGE_IMAGES_CONTAINER'
+            value: 'generated-images'
+          }
           {
             name: 'BACKEND_URL'
             value: 'https://${containerAppName}.${containerAppEnvironment.outputs.defaultDomain}'

infra/bicep/main.bicep

@@ -762,6 +762,10 @@ module mcp_container_app './modules/compute/container-app.bicep' = {
             name: 'AZURE_STORAGE_BLOB_URL'
             value: storage_account.outputs.blobEndpoint
           }
+          {
+            name: 'AZURE_STORAGE_IMAGES_CONTAINER'
+            value: storageContainerNameGeneratedImages
+          }
           {
             name: 'BACKEND_URL'
             value: 'https://${backendContainerAppName}.${container_app_environment.outputs.defaultDomain}'