Added

• /vdt doctor. One look at everything that commonly goes wrong, in a single list: platform and scheduler, whether the plugin is enabled, MSPT thresholds that leave no gap, worlds with a minimum above their maximum, worlds that are configured but not loaded, other plugins that keep overwriting a world's distances (with the likely culprits), the per-world MSPT state, free heap, PlaceholderAPI and whether an update is out. It reads only and changes nothing. Pasting its output into a bug report answers most of the first questions. Permission: the same as /vdt status.
• /vdt analyze and /vdt doctor are listed in /vdt help.

Changed

• The readme and the project page now describe the client view distance cap and the conflict detection from the 2.11 and 2.12 releases, and list the placeholders only once.

No config changes. messages.yml gains a doctor section; an existing file keeps working, the new lines fall back to the bundled English text.