fix(engines): the Full Sweep and Passive Recon presets named a hidden stage

preset_stages walked every stage in the registry, asset_seed included.
That stage is the focused-rescan seed and is deliberately catalog_hidden,
so any preset that flipped it off its default emitted
{"asset_seed": {"enabled": …}} and _validate_stages refused the create
with "Unknown stage 'asset_seed'".

Full Sweep and Passive Recon both flip it; Standard sends {} and Blank
agrees with its default, which is why only those two failed.

Apply the filter the catalog and the YAML export already use.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018ASYBQe7daGgrKcYCav6rP

stages/presets.py

@@ -50,7 +50,7 @@ def preset_stages(name: str) -> dict[str, dict]:
     return {
         spec.name: {"enabled": _enabled(name, spec)}
         for spec in stages()
-        if _enabled(name, spec) != spec.defaults["enabled"]
+        if not spec.catalog_hidden and _enabled(name, spec) != spec.defaults["enabled"]
     }