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/plugin/tool-registry.ts

@@ -29,6 +29,7 @@ import {
   createTaskList,
   createTaskUpdateTool,
   createHashlineEditTool,
+  createPrepareCouncilPromptTool,
 } from "../tools"
 import { getMainSessionID } from "../features/claude-code-session-state"
 import { filterDisabledTools } from "../shared/disabled-tools"
@@ -278,6 +279,7 @@ export function createToolRegistry(args: {
     ...(interactiveBashEnabled ? { interactive_bash: factories.interactive_bash } : {}),
     ...taskToolsRecord,
     ...hashlineToolsRecord,
+    prepare_council_prompt: createPrepareCouncilPromptTool(),
   }
 
   for (const toolDefinition of Object.values(allTools)) {