feat(02-01): add athena council execution primitives

- Add council execution result and member response types for orchestration
- Implement provider/model parser for BackgroundManager-compatible model input
- Add shared council prompt builder and export new athena modules

src/agents/athena/model-parser.ts

@@ -0,0 +1,23 @@
+export interface ParsedModel {
+  providerID: string
+  modelID: string
+}
+
+export function parseModelString(model: string): ParsedModel | null {
+  if (!model) {
+    return null
+  }
+
+  const slashIndex = model.indexOf("/")
+  if (slashIndex <= 0) {
+    return null
+  }
+
+  const providerID = model.substring(0, slashIndex)
+  const modelID = model.substring(slashIndex + 1)
+  if (!modelID) {
+    return null
+  }
+
+  return { providerID, modelID }
+}