fix(athena): address 5 audit findings — remove harmful thinking config, add error handling, improve tests

- Remove applyModelThinkingConfig and all callers (OpenCode handles thinking natively)

- Add try/catch error handling to prepare_council_prompt filesystem operations

- Add mode input validation to prepare_council_prompt tool

- Add 2 missing placeholder test cases (RETRY_FAILED_IF_OTHERS_FINISHED, CANCEL_RETRYING_ON_QUORUM)

- Remove redundant 'Do NOT use TodoWrite' prompt section from council member agent

src/agents/athena/athena-config-injection.test.ts

@@ -21,6 +21,14 @@ describe("Athena prompt config injection placeholders", () => {
       it("#then contains timeout reference with 30000", () => {
         expect(athenaConfig.prompt).toContain("30000")
       })
+
+      it("#then contains RETRY_FAILED_IF_OTHERS_FINISHED placeholder", () => {
+        expect(athenaConfig.prompt).toContain("{RETRY_FAILED_IF_OTHERS_FINISHED}")
+      })
+
+      it("#then contains CANCEL_RETRYING_ON_QUORUM placeholder", () => {
+        expect(athenaConfig.prompt).toContain("{CANCEL_RETRYING_ON_QUORUM}")
+      })
     })
   })
 })