feat: Add SvelteKit web app with scan sessions and import queue

Replaces the Flask/Alpine web app with a SvelteKit 2 + Svelte 5 rewrite
under web/, built on adapter-node and Tailwind v4. Same shape as the
reference b4l budget app — no auth, stateless pass-through to InvenTree.

New "scan session" flow groups mass scans into a session with live
counters (scanned / succeeded / pending / failed). Unknown parts in
import mode are fed to a worker pool that spawns inventree-part-import
(IMPORT_CONCURRENCY, default 3, with 3-retry). Anything that can't be
resolved automatically — parse errors, missing qty, invalid location,
API errors, or imports that exhaust retries — drops into a Failures
panel with a per-item Fix dialog (edit fields / search existing part /
retry import). CSV export on the failure list.

Layout is two-column on lg+: scanner + activity on the left, pending
imports + failures on the right. Light-theme default. SSE on
/api/events streams session and import events to the client.

Barcode parser ported from the Python/JS versions and hardened for
Digi-Key MH10.8.2 barcodes both with and without GS separators (old
parser greedy-matched Q's digits and read "Q6" + "11ZPICK" as 611).
Import worker also now treats a subprocess failure followed by a
successful findPart as a success, so partial imports (part created but
a duplicate parameter trips the DB constraint) no longer land in the
Failures panel.

Deploy artifacts: systemd unit, nginx example (SSE-friendly), and a
step-by-step deploy/README. Requires inventree-part-import >= 1.9.2 on
the server for InvenTree 1.x API compatibility.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/vite.config.ts

@@ -0,0 +1,7 @@
+import { sveltekit } from '@sveltejs/kit/vite';
+import tailwindcss from '@tailwindcss/vite';
+import { defineConfig } from 'vite';
+
+export default defineConfig({
+	plugins: [tailwindcss(), sveltekit()]
+});