fix: run migrations on boot and stop failures rendering as empty (#23)

The storefront showed no inventory after deploying the categories/tags
release. No data was lost: the code queried categories/item_tags/
items.category_id against a database where the migration had not been
run, and that failure was invisible at every layer.

Three changes, each addressing one layer:

Migrations now run at container start, so deployed code cannot be ahead
of the schema and the easily-forgotten manual `docker exec migrate.js
up` step disappears. migrate.js waits for Postgres to accept
connections first, since the NAS brings the DB container up slower than
the app, and still exits non-zero so a bad migration stops the
container rather than serving a half-migrated schema.

Express 4 does not forward a rejected async handler, and no error
middleware was mounted, so a failing query never responded at all. Async
routes are now wrapped and an error middleware guarantees a 500. A hung
request is indistinguishable from an empty result in the UI, which is
how a schema mismatch came to read as "the store has no items".

The storefront now separates "request failed" from "no items" and offers
a retry. fetchItems/fetchFilterOptions throw on a non-OK response rather
than returning the parsed error body, which would have been set as the
item list and crashed the grid on .map.

Also restores the project-context update from 7fb5764, which was left
out of PR #24 and ended up dangling.

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

frontend/src/App.tsx

@@ -1,5 +1,5 @@
 import { useEffect, useState, useCallback, useMemo } from 'react';
-import { Layout, Typography, Switch, Row, Col, Spin, Button, theme, Badge, Empty } from 'antd';
+import { Layout, Typography, Switch, Row, Col, Spin, Button, theme, Badge, Empty, Alert } from 'antd';
 import { ShoppingCartOutlined, FilterOutlined } from '@ant-design/icons';
 import { Link, useSearchParams } from 'react-router-dom';
 import { Item, FilterOptions, fetchItems, fetchFilterOptions } from './api';
@@ -27,6 +27,7 @@ const FILTER_DEBOUNCE_MS = 250;
 export default function App() {
   const [items, setItems] = useState<Item[]>([]);
   const [loading, setLoading] = useState(true);
+  const [failed, setFailed] = useState(false);
   const [options, setOptions] = useState<FilterOptions | null>(null);
   const [drawerOpen, setDrawerOpen] = useState(false);
   const [searchParams, setSearchParams] = useSearchParams();
@@ -55,7 +56,14 @@ export default function App() {
 
   const load = useCallback(() => {
     return fetchItems(filtersFromSearchParams(new URLSearchParams(filterKey)))
-      .then(setItems)
+      .then((loaded) => {
+        setItems(loaded);
+        setFailed(false);
+      })
+      // A failed request must never fall through to the empty state: telling a
+      // customer "no items yet" when the server is broken hides the outage and
+      // reads as an empty shop.
+      .catch(() => setFailed(true))
       .finally(() => setLoading(false));
   }, [filterKey]);
 
@@ -124,8 +132,16 @@ export default function App() {
           />
         </div>
 
-        {loading && !items.length ? <Spin /> : null}
-        {!loading && !items.length ? (
+        {loading && !items.length && !failed ? <Spin /> : null}
+        {failed ? (
+          <Alert
+            type="error"
+            showIcon
+            message="Couldn't load items"
+            description="The server didn't return the catalogue. This is usually temporary."
+            action={<Button size="small" onClick={() => { setLoading(true); load(); }}>Retry</Button>}
+          />
+        ) : !loading && !items.length ? (
           <Empty
             description={
               hasActiveFilters(filters)