refactor(athena): remove redundant council_read tool, use Read instead

council_read was a sandboxed readFile wrapper for .sisyphus/ archives.
Now that council_finalize extracts member responses into plain files,
the standard Read tool serves the same purpose. Removes the tool, its
tests, and updates Athena's prompt to reference Read directly.

src/plugin/tool-registry.ts

@@ -31,7 +31,7 @@ import {
   createHashlineEditTool,
   createPrepareCouncilPromptTool,
 } from "../tools"
-import { createCouncilFinalize, createCouncilRead } from "../tools/council-archive"
+import { createCouncilFinalize } from "../tools/council-archive"
 import { contextCollector } from "../features/context-injector"
 import { getMainSessionID } from "../features/claude-code-session-state"
 import { filterDisabledTools } from "../shared/disabled-tools"
@@ -283,7 +283,6 @@ export function createToolRegistry(args: {
     ...hashlineToolsRecord,
     prepare_council_prompt: createPrepareCouncilPromptTool(ctx.directory),
     council_finalize: createCouncilFinalize(ctx.directory, { contextCollector }),
-    council_read: createCouncilRead(ctx.directory),
   }
 
   for (const toolDefinition of Object.values(allTools)) {