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>

backend/tests/unit/asyncRoute.test.ts

@@ -0,0 +1,44 @@
+import { Request, Response, NextFunction } from 'express';
+import { asyncRoute } from '../../src/asyncRoute';
+
+function fakeArgs() {
+  const next = jest.fn() as unknown as NextFunction;
+  return { req: {} as Request, res: {} as Response, next };
+}
+
+describe('asyncRoute', () => {
+  it('passes a rejected handler to next so Express can answer the request', async () => {
+    const boom = new Error('relation "categories" does not exist');
+    const { req, res, next } = fakeArgs();
+
+    await asyncRoute(async () => { throw boom; })(req, res, next);
+
+    expect(next).toHaveBeenCalledWith(boom);
+  });
+
+  it('passes a synchronous throw to next as well', async () => {
+    const boom = new Error('sync failure');
+    const { req, res, next } = fakeArgs();
+
+    await asyncRoute(() => { throw boom; })(req, res, next);
+
+    expect(next).toHaveBeenCalledWith(boom);
+  });
+
+  it('leaves a successful handler alone', async () => {
+    const { req, res, next } = fakeArgs();
+
+    await asyncRoute(async () => 'fine')(req, res, next);
+
+    expect(next).not.toHaveBeenCalled();
+  });
+
+  it('forwards the same arguments it was given', async () => {
+    const handler = jest.fn(async () => undefined);
+    const { req, res, next } = fakeArgs();
+
+    await asyncRoute(handler)(req, res, next);
+
+    expect(handler).toHaveBeenCalledWith(req, res, next);
+  });
+});