feat(11-05): add mode parameter to spawnAgent procedure

- Update spawnAgentInputSchema to include optional mode field
- Pass mode through to agentManager.spawn() for mode-aware spawning

src/trpc/router.ts

@@ -103,6 +103,8 @@ export const spawnAgentInputSchema = z.object({
   prompt: z.string().min(1),
   /** Optional working directory (defaults to worktree path) */
   cwd: z.string().optional(),
+  /** Agent operation mode (defaults to 'execute') */
+  mode: z.enum(['execute', 'discuss', 'breakdown']).optional(),
 });
 
 export type SpawnAgentInput = z.infer<typeof spawnAgentInputSchema>;
@@ -355,6 +357,7 @@ export const appRouter = router({
         taskId: input.taskId,
         prompt: input.prompt,
         cwd: input.cwd,
+        mode: input.mode,
       });
     }),