refactor(schema): replace deprecated .merge() with .extend() and add council-member override

Replace deprecated Zod .merge(z.object({...})) with .extend({...}) for AthenaOverrideConfigSchema. Add council-member to AgentOverridesSchema to match OverridableAgentNameSchema.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/config/schema/agent-overrides.ts

@@ -56,11 +56,9 @@ export const AgentOverrideConfigSchema = z.object({
     .optional(),
 })
 
-export const AthenaOverrideConfigSchema = AgentOverrideConfigSchema.merge(
-  z.object({
-    council: AthenaConfigSchema.shape.council.optional(),
-  })
-)
+export const AthenaOverrideConfigSchema = AgentOverrideConfigSchema.extend({
+  council: AthenaConfigSchema.shape.council.optional(),
+})
 
 export const AgentOverridesSchema = z.object({
   build: AgentOverrideConfigSchema.optional(),
@@ -77,6 +75,7 @@ export const AgentOverridesSchema = z.object({
   explore: AgentOverrideConfigSchema.optional(),
   "multimodal-looker": AgentOverrideConfigSchema.optional(),
   atlas: AgentOverrideConfigSchema.optional(),
+  "council-member": AgentOverrideConfigSchema.optional(),
   athena: AthenaOverrideConfigSchema.optional(),
 })