fix(athena): address 6 council review findings — launcher, schema, filtering, presentation

- Forward temperature and permission through council-launcher to background manager
- Add LaunchInput.temperature and LaunchInput.permission to background-agent types
- Extract session guard with 5-minute timeout to prevent stale council locks
- Make council optional in AthenaOverrideConfigSchema for partial user overrides
- Support member lookup by both name and model ID in filterCouncilMembers
- Add provider/model-id format validation to CouncilMemberSchema
- Fix findings-presenter group header to show finding count instead of first finding's reporter count

src/config/schema/athena.ts

@@ -1,7 +1,19 @@
 import { z } from "zod"
 
+/** Validates model string format: "provider/model-id" (e.g., "openai/gpt-5.3-codex"). */
+const ModelStringSchema = z
+  .string()
+  .min(1)
+  .refine(
+    (model) => {
+      const slashIndex = model.indexOf("/")
+      return slashIndex > 0 && slashIndex < model.length - 1
+    },
+    { message: 'Model must be in "provider/model-id" format (e.g., "openai/gpt-5.3-codex")' }
+  )
+
 export const CouncilMemberSchema = z.object({
-  model: z.string(),
+  model: ModelStringSchema,
   temperature: z.number().min(0).max(2).optional(),
   variant: z.string().optional(),
   name: z.string().optional(),