fix(admin): theme, American English, and inventory/reservation tooling (#27)

Seven reported items, of which the first four had two root causes.

The active tab was invisible in dark mode because colorPrimary was
hardcoded to #1a1a1a in both themes. The accent now inverts with the
theme, and colorTextLightSolid inverts with it, or a near-white accent
would get antd's default white label and disappear.

The Category tab, Tag tab, and item-form category selector ignored the
theme entirely. antd declares main: lib/index.js and module: es/index.js,
so importing from 'antd' resolves to the ES build while 'antd/lib/...'
loads the CommonJS one — two copies, two React contexts, and no
ConfigProvider for anything deep-imported. Switching those files to
antd/es/* keeps the deep-import convention and shares the instance. This
was introduced by my own use of the lib path; es is correct under Vite.
Two storefront components had the same latent bug.

"Colour" is now "Color".

The Customers tab shows how many items each customer is holding, as a
link opening the item list with a Release button. Release mirrors the
customer's own cart removal — drop the cart row, return the item to
available, guarded on 'reserved' so it can never resurrect a sold item —
and deliberately sends no email about an action the customer did not
take. The count is a subquery rather than another join, which would have
multiplied rows and inflated order_count and total_spent_cents.

The Inventory tab filters by category, tags, price, and status, reusing
the storefront's parser and query builder so the two cannot drift.
Reserved is one option in a Status filter rather than a standalone toggle.

Also fixes two defects the screenshots exposed: the reserved-count link
bubbled to the row handler and opened the customer drawer behind the
dialog, and .admin-category-node had no CSS at all, so the tree node name,
item count, and actions ran together as one string.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frontend/src/main.tsx

@@ -16,6 +16,11 @@ import { CartProvider } from './cart/CartContext';
 import { ThemeModeProvider, useThemeMode } from './theme/ThemeContext';
 import './styles.css';
 
+// The brand accent is monochrome, so it inverts between themes rather than
+// switching to a different hue.
+const LIGHT_ACCENT = '#1a1a1a';
+const DARK_ACCENT = '#f0f0f0';
+
 const REDUCED_MOTION_QUERY = '(prefers-reduced-motion: reduce)';
 
 // Respects the OS-level "reduce motion" accessibility setting by turning off
@@ -44,7 +49,17 @@ function Root() {
     <ConfigProvider
       theme={{
         algorithm: mode === 'dark' ? antdTheme.darkAlgorithm : antdTheme.defaultAlgorithm,
-        token: { colorPrimary: '#1a1a1a', motion: !prefersReducedMotion }
+        token: {
+          // The accent inverts with the theme rather than staying near-black.
+          // Held constant, it rendered the active tab label in #1a1a1a on a
+          // dark background — invisible.
+          colorPrimary: mode === 'dark' ? DARK_ACCENT : LIGHT_ACCENT,
+          // Text drawn *on* the accent (primary buttons, selected rows) has to
+          // invert with it too, or a near-white accent gets antd's default
+          // white label and disappears.
+          colorTextLightSolid: mode === 'dark' ? LIGHT_ACCENT : '#ffffff',
+          motion: !prefersReducedMotion
+        }
       }}
     >
       <BrowserRouter>