feat(athena): add prepare_council_prompt tool for faster council launches

Athena saves the analysis prompt to a temp file once, then launches each
council member with a short "Read <path> for your instructions" prompt.
This eliminates repeated prompt text across N task calls while preserving
individual clickable task panes in the TUI.

src/tools/index.ts

@@ -46,6 +46,7 @@ export {
   createTaskUpdateTool,
 } from "./task"
 export { createHashlineEditTool } from "./hashline-edit"
+export { createPrepareCouncilPromptTool } from "./prepare-council-prompt"
 
 export function createBackgroundTools(manager: BackgroundManager, client: OpencodeClient): Record<string, ToolDefinition> {
   const outputManager: BackgroundOutputManager = manager