fix(build): use zod v3 two-arg form for z.record in agent schema

zod 3.25 (the version resolved by ^3.25.0) requires z.record() to take
both a key and a value schema. The single-arg form z.record(z.unknown())
is zod v4 syntax, which trips next build's typecheck.

Four call sites in packages/shared/src/schemas/agent.ts were written in
v4 form (lines 39, 41, 73, 74). This is a pure type-only fix — runtime
behavior is identical.

packages/shared/src/schemas/agent.ts

@@ -36,9 +36,9 @@ export const agentTaskSchema = z.object({
   id: z.string(),
   agent_id: z.string(),
   task_type: z.string(),
-  input: z.record(z.unknown()),
+  input: z.record(z.string(), z.unknown()),
   status: z.enum(['pending', 'running', 'completed', 'failed']).default('pending'),
-  output: z.record(z.unknown()).optional(),
+  output: z.record(z.string(), z.unknown()).optional(),
   error_message: z.string().optional(),
   started_at: z.string().datetime().optional(),
   completed_at: z.string().datetime().optional(),
@@ -70,8 +70,8 @@ export const agentSchema = z.object({
   last_active_at: z.string().datetime().optional(),
   domain: z.string(),
   tags: z.array(z.string()).default([]),
-  config: z.record(z.unknown()).optional(),
-  custom_fields: z.record(z.unknown()).optional(),
+  config: z.record(z.string(), z.unknown()).optional(),
+  custom_fields: z.record(z.string(), z.unknown()).optional(),
   created: z.string().datetime(),
   updated: z.string().datetime(),
 });