feat: cw task add CLI command + {AGENT_ID} prompt placeholder

- Add `createTaskForAgent` tRPC mutation: resolves agent → task → phase, creates sibling task
- Add `cw task add <name> --agent-id <id>` CLI command
- Replace `{AGENT_ID}` and `{AGENT_NAME}` placeholders in writeInputFiles() before flushing
- Update docs/agent.md and docs/cli-config.md

apps/server/trpc/routers/task.ts

@@ -11,6 +11,7 @@ import {
   requirePhaseRepository,
   requireDispatchManager,
   requireChangeSetRepository,
+  requireAgentManager,
 } from './_helpers.js';
 
 export function taskProcedures(publicProcedure: ProcedureBuilder) {
@@ -213,5 +214,55 @@ export function taskProcedures(publicProcedure: ProcedureBuilder) {
         return edges;
       }),
 
+    createTaskForAgent: publicProcedure
+      .input(z.object({
+        agentId: z.string().min(1),
+        name: z.string().min(1),
+        description: z.string().optional(),
+        category: z.enum(['execute', 'research', 'discuss', 'plan', 'detail', 'refine', 'verify', 'merge', 'review']).optional(),
+      }))
+      .mutation(async ({ ctx, input }) => {
+        const agentManager = requireAgentManager(ctx);
+        const taskRepository = requireTaskRepository(ctx);
+
+        const agent = await agentManager.get(input.agentId);
+        if (!agent) {
+          throw new TRPCError({
+            code: 'NOT_FOUND',
+            message: `Agent '${input.agentId}' not found`,
+          });
+        }
+        if (!agent.taskId) {
+          throw new TRPCError({
+            code: 'BAD_REQUEST',
+            message: `Agent '${agent.name}' has no assigned task`,
+          });
+        }
+
+        const agentTask = await taskRepository.findById(agent.taskId);
+        if (!agentTask) {
+          throw new TRPCError({
+            code: 'NOT_FOUND',
+            message: `Agent's task '${agent.taskId}' not found`,
+          });
+        }
+        if (!agentTask.phaseId) {
+          throw new TRPCError({
+            code: 'BAD_REQUEST',
+            message: `Agent's task has no phase — cannot create sibling task`,
+          });
+        }
+
+        return taskRepository.create({
+          phaseId: agentTask.phaseId,
+          initiativeId: agentTask.initiativeId,
+          name: input.name,
+          description: input.description ?? null,
+          category: input.category ?? 'execute',
+          type: 'auto',
+          status: 'pending',
+        });
+      }),
+
   };
 }