feat(skill): layer the host skill registry per scope like the tools registry

The skills capability moves back to the host plane as one singleton, layered
with the ScopedLayers infrastructure the tools registry established: a
registration files into its calling context's layer (repository plugins and
host rows land global, a preset's skill-local lands in that preset's layer),
and a read merges the global layer with the viewing scope's chain, the
nearest layer winning duplicate names outright while rank keeps deciding
duplicates within one layer.

The web-app bundle re-enables the base skill registry row (skill-local and
tool-skill stay preset-owned), the standard preset drops its isolate skills
realm for bare rows over the host registry, tool-skill passes the calling
agent as the view scope, and the gateway's skills domain reads the host
registry in the presenter scope — a cold session now resolves its recorded
preset's standing key instead of failing.

packages/bundle/web-app/cordis.patch.yml

@@ -228,8 +228,14 @@
 - id: tool-str-replace-editor
   disabled: true
 
-- id: skill
-  disabled: true
+# The `skill` REGISTRY stays in the host plane. It is host+per-scope layered
+# (the tools-registry shape): deployment-level providers — repository plugins,
+# a host skill-local row — register into its global layer, while a preset's
+# `skill-local` registers into that preset's layer, and each agent reads the
+# merged catalog its scope chain selects. Only the per-agent rows move behind
+# presets: the base host `skill-local` row is disabled here (presets own local
+# discovery), and `tool-skill` is what a preset mounts to give its agent the
+# catalog and loader at all.
 
 - id: skill-local
   disabled: true