feat(rust): mod configuration from the site, and an editor that will not rewrite a float

R18's two tiers: a form generated from a config file's own values, and raw JSON
for what a form cannot express. Admin → Rust mod config, one live round trip per
action, nothing cached between a browser and a game host's disk.

`configEdit.js` is the part that could not be done naively. JavaScript cannot
tell `1` from `1.0`, and both mod frameworks deserialize a config into typed C#
classes — so a read-modify-write silently rewrites every whole-numbered float as
an integer on fields nobody touched, and a plugin that then throws at load does
not come back. It never parses, mutates and re-serialises: it records the SOURCE
SPAN of every value and splices literals into them, so an untouched `1.0` is
still `1.0` and a number an admin types travels as text the whole way (D35/D36).

The bridge's own config is editable with `Host`, `Port` and `ServerId` locked,
in the form and in the raw tier, because either would cut the link carrying the
edit or strand every row this site holds (D38). Credentials render masked with a
reveal; the raw tier shows them (D37) and the audit trail never does.

`rust_config_writes` records every save including the refused and the rolled
back — an operator asking why a setting is not what they set needs to see that
somebody tried.

Three defects a browser walk found that 179 green tests did not:

* every save of the bridge's own config was refused while the page said the
  opposite — a `<select>` whose value matches no `<option>` shows the first one,
  so the reload guess `RunicGateway` was on the wire and "nothing" was on the
  screen;
* `btn ghost` is not a class this platform defines (`.btn-ghost` is), so every
  secondary button in this module has rendered as a primary one since phase 7 —
  here it made the open file and the active tier indistinguishable;
* a save's refusal rendered at the top of a long form, far from the button.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PMH6bw1jXMgbyF3ZWGEzSM

client/src/entry.jsx

@@ -22,9 +22,10 @@ import Servers from './routes/public/Servers.jsx'
 import ServerDetail from './routes/public/ServerDetail.jsx'
 import Account from './routes/player/Account.jsx'
 import Permissions from './routes/admin/Permissions.jsx'
+import ModConfig from './routes/admin/ModConfig.jsx'
 import UserRustSections from './routes/admin/UserRustSections.jsx'
 import FooterStatus from './components/FooterStatus.jsx'
-import { IconKey, IconLink } from './icons.jsx'
+import { IconKey, IconLink, IconSliders } from './icons.jsx'
 
 // The module id, exactly as `module.json` spells it. Core keys the registry by it
 // and prefixes every route path with it.
@@ -82,7 +83,18 @@ registry.registerRoutes(ID, {
     { path: 'servers/:id', element: <ServerDetail /> },
   ],
   player: [{ path: '', element: <Account /> }],
-  admin: [{ path: '', element: <Permissions /> }],
+  admin: [
+    { path: '', element: <Permissions /> },
+    // Phase 7b (R18). A second admin page rather than a tab on the first: the
+    // permission mirror decides who may do what inside the game, and this edits
+    // the game host's own files. They are neighbours, not halves of one screen,
+    // and the nav says so with two rows.
+    //
+    // A static segment under the module's namespace, so it lands at
+    // `/admin/rust/config` and core's admin gate applies to it exactly as it
+    // does to the page above.
+    { path: 'config', element: <ModConfig /> },
+  ],
 })
 
 // ── Nav ───────────────────────────────────────────────────────────────────
@@ -127,7 +139,10 @@ registry.registerNav(ID, {
 // every sidebar row, and the one without is the only text in a column of glyphs.
 registry.registerNav(ID, {
   area: 'admin',
-  items: [{ label: 'Rust permissions', to: '/admin/rust', icon: IconKey }],
+  items: [
+    { label: 'Rust permissions', to: '/admin/rust', icon: IconKey },
+    { label: 'Rust mod config', to: '/admin/rust/config', icon: IconSliders },
+  ],
 })
 
 // ── Extension slots ───────────────────────────────────────────────────────