feat(rust): zone presets, and the zone step's options, messages and dome (PLAN_REDESIGNS §3, D210)

Admin → Rust zone presets: named sets of ZoneManager flags and settings for
one server, several, or every server (D195), ticked in groups read from each
server's own ZoneManager list in its last hello (D211). A flag not on a
covered server is refused on save with the server named; two presets of one
name may not share a server.

rust.zone.open gains options (one line, NoBuild, radiation=10), enterMessage,
leaveMessage, delivery, dome and domeStack. The options field's dropdown is
rust.options.zone_presets, whose row VALUE is the preset's line, so picking
one copies it into the step (D210) and no published event changes when a
preset does. The line and the dome are checked against the server's hello
on save and in a dry run; bad-option and dome-unavailable are permanent.

Schema: rust_zone_presets, rust_zone_preset_servers. Swagger fragment and
routes.manifest regenerated against the pinned core f0e7d2a.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

client/src/icons.jsx

@@ -111,3 +111,16 @@ export const IconServer = () => (
 )
 
 export default { IconLink, IconKey, IconSliders, IconEye, IconServer }
+
+/**
+ * A circle inside a dashed ring — the admin sidebar's row for zone presets.
+ *
+ * A zone is an area with rules at its edge, so the glyph is a place and its
+ * boundary rather than a map pin, which the live map already means.
+ */
+export const IconZone = () => (
+  <Icon>
+    <circle cx="12" cy="12" r="9" strokeDasharray="3 3" />
+    <circle cx="12" cy="12" r="3" />
+  </Icon>
+)