feat: add background agents with scheduling support

- Add background task scheduling system with cron-based triggers
- Add background-task-detail component for viewing agent status
- Add agent schedule repo and state management
- Update sidebar to show background agents section
- Remove old workflow-authoring and workflow-run-ops skills
- Add IPC handlers for agent schedule operations

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/x/packages/shared/src/agent-schedule.ts

@@ -0,0 +1,44 @@
+import z from "zod";
+
+// Cron schedule - runs at exact times defined by cron expression.
+// Examples:
+//   - Every 5 minutes: "*/5 * * * *"
+//   - Everyday at 8am: "0 8 * * *"
+//   - Every Monday at 9am: "0 9 * * 1"
+export const CronSchedule = z.object({
+    type: z.literal("cron"),
+    expression: z.string(),
+});
+
+// Window schedule - runs once during a time window.
+// The agent will run once at a random time within the specified window.
+// Examples:
+//   - Daily between 8am and 10am: cron="0 0 * * *", startTime="08:00", endTime="10:00"
+//   - Weekly on Monday between 9am-12pm: cron="0 0 * * 1", startTime="09:00", endTime="12:00"
+export const WindowSchedule = z.object({
+    type: z.literal("window"),
+    cron: z.string(), // Base frequency cron expression
+    startTime: z.string(), // "HH:MM" format
+    endTime: z.string(), // "HH:MM" format
+});
+
+// Once schedule - runs exactly once at a specific time, then never again.
+// Examples:
+//   - Run once at specific datetime: runAt="2024-02-05T10:30:00"
+export const OnceSchedule = z.object({
+    type: z.literal("once"),
+    runAt: z.string(), // ISO 8601 datetime (local time, e.g., "2024-02-05T10:30:00")
+});
+
+export const ScheduleDefinition = z.union([CronSchedule, WindowSchedule, OnceSchedule]);
+
+export const AgentScheduleEntry = z.object({
+    schedule: ScheduleDefinition,
+    enabled: z.boolean().optional().default(true),
+    startingMessage: z.string().optional(), // Message sent to agent when run starts (defaults to "go")
+    description: z.string().optional(), // Brief description of what the agent does (for UI display)
+});
+
+export const AgentScheduleConfig = z.object({
+    agents: z.record(z.string(), AgentScheduleEntry),
+});