Add manual scheduled task entry

Lets users log tasks the Linux agent can't discover on its own (e.g.
Docker-based backup jobs) directly in the UI. Tasks now carry an
origin ('agent' | 'manual') so the agent's report-sync logic only
ever creates/updates/stale-marks agent-sourced rows, leaving manual
entries untouched; the API rejects edits/deletes of agent-sourced
tasks to keep that boundary enforced server-side too.

server/src/services/taskSync.ts

@@ -22,7 +22,7 @@ export async function syncServerTasks(serverId: number, report: AgentReport) {
   const now = new Date().toISOString();
 
   const existing = await db.query.scheduledTasks.findMany({
-    where: eq(scheduledTasks.serverId, serverId),
+    where: and(eq(scheduledTasks.serverId, serverId), eq(scheduledTasks.origin, "agent")),
   });
 
   const seenIds: number[] = [];
@@ -56,6 +56,7 @@ export async function syncServerTasks(serverId: number, report: AgentReport) {
         .values({
           serverId,
           scheduleType: task.scheduleType,
+          origin: "agent",
           name: task.name,
           command: task.command,
           scheduleExpression: task.scheduleExpression,
@@ -71,15 +72,17 @@ export async function syncServerTasks(serverId: number, report: AgentReport) {
     }
   }
 
-  // Anything belonging to this server that wasn't in this report is now stale,
-  // rather than deleted, so a bad/partial agent run doesn't wipe history.
+  // Anything agent-sourced for this server that wasn't in this report is now stale,
+  // rather than deleted, so a bad/partial agent run doesn't wipe history. Manually
+  // entered tasks (origin = 'manual') are never touched by agent sync.
+  const agentScope = and(eq(scheduledTasks.serverId, serverId), eq(scheduledTasks.origin, "agent"));
   if (seenIds.length > 0) {
     await db
       .update(scheduledTasks)
       .set({ isStale: true })
-      .where(and(eq(scheduledTasks.serverId, serverId), notInArray(scheduledTasks.id, seenIds)));
+      .where(and(agentScope, notInArray(scheduledTasks.id, seenIds)));
   } else {
-    await db.update(scheduledTasks).set({ isStale: true }).where(eq(scheduledTasks.serverId, serverId));
+    await db.update(scheduledTasks).set({ isStale: true }).where(agentScope);
   }
 
   await db