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/drizzle/meta/_journal.json

@@ -8,6 +8,13 @@
       "when": 1783628241015,
       "tag": "0000_aspiring_blink",
       "breakpoints": true
+    },
+    {
+      "idx": 1,
+      "version": "6",
+      "when": 1783634598855,
+      "tag": "0001_amazing_greymalkin",
+      "breakpoints": true
     }
   ]
 }