permissions: a plugin can mark part of its surface owner-only

A plugin worth granting to a Member can also hold the credential the rest of it runs on. Jellyfin's
/_config stores a server's admin token and drives account provisioning; the rest of the plugin is
exactly what a Member should have. The choice was all of it or none of it.

`ownerOnly` on a plugin permission takes sub-paths relative to the mount prefix. The permission stays
fully grantable — this is not the ownerOnly PERMISSION that manifest.ts refuses, and that refusal
still stands: a permission nobody can delegate is a contradiction. This says a few paths administer
the plugin rather than use it.

Declared by the plugin, enforced by the platform. A plugin could check this itself and the first one
would; the tenth would add a route and forget, with no boot failure and no warning — the shape
assertPermissionTotality exists to prevent. In the gate it is enforced once, on the door they all
pass through, and a route added later by someone who never read the manifest is covered by default.

Checked before selfService and before kind. A path that is somehow both self-service and owner-only
is a contradiction, and the safe reading has to win. A write grant does not unlock it either — level
is not the question this answers.

Also forwards X-Officer-Owner and X-Officer-Level to a sidecar whose proxy names its permission key,
for the finer decisions the platform cannot make for it: whose rows a read returns, which fields a
level may see. Facts, never the role name — a plugin branching on "Super Admin" would give every
plugin repository an opinion about the platform's role vocabulary, and renaming a role would change
authorization in code the platform does not own. These are safe to trust only because the proxy
copies a three-item allowlist off the inbound request; that is now written where it would be changed.

The owner's level is reported as write rather than the absent 'none': they hold everything implicitly
and appear in no grants map, so the raw lookup inverts the meaning for the one account that can do
anything.

No plugin declares one yet. Jellyfin cannot until connections stop being per-user — locking /_config
today leaves a Member with a plugin that only shows a connect form they may not submit.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/servers/plugins/mount.ts

@@ -139,6 +139,10 @@ function pluginPermissions(state: PluginState): Permission[] {
     api: index === 0 ? [prefix] : [],
     routes: index === 0 ? [prefix] : [],
     ...(permission.readOnlyWrites ? { readOnlyWrites: permission.readOnlyWrites } : {}),
+    // Only meaningful on the entry that claims the paths — a later permission claims no `api`, so an
+    // `ownerOnly` on it would match nothing. Threaded anyway rather than dropped: silently ignoring a
+    // declaration is how a plugin author concludes the field does not work.
+    ...(permission.ownerOnly ? { ownerOnly: permission.ownerOnly } : {}),
   }));
 }