test(cli): add TODO comment and locked-remote-DB test script

- Add inline TODO comment in runCommand.ts about standardising
  replication failure cause identification logic.
- Add test-sync-locked-remote-linux.sh that verifies:
  1. sync succeeds when the remote milestone is not locked.
  2. sync fails with an actionable error when the remote milestone
     has locked=true and accepted_nodes is empty.

src/apps/cli/commands/runCommand.ts

@@ -22,6 +22,9 @@ export async function runCommand(options: CLIOptions, context: CLICommandContext
         console.log("[Command] sync");
         const result = await core.services.replication.replicate(true);
         if (!result) {
+            // TODO: Standardise the logic for identifying the cause of replication
+            // failure so that every reason (locked DB, version mismatch, network
+            // error, etc.) is surfaced with a CLI-specific actionable message.
             const replicator = core.services.replicator.getActiveReplicator();
             if (replicator?.remoteLockedAndDeviceNotAccepted) {
                 console.error(