feat(web): serve the web app under /app and send every billing link there (WS-B)

apps/web was never deployed, so /billing on the public domain returned the
landing page and d3ro.dev (desktop "upgrade") did not resolve.

- apps/web runs with basePath /app and output standalone; /download and
  /releases redirect to the site's #download. A Dockerfile and a d3ro-web
  compose service (port 3002) deploy it to the NAS with the other images.
- The site bridge worker forwards /app/* to WEB_APP_ORIGIN (the tunnel host)
  and rewrites upstream redirects; everything else still goes to Pages.
  With no origin configured /app answers 503 instead of the landing page.
- Desktop upgrade, desktop Stripe return, mobile subscription management,
  the web checkout/portal returns and the site all use billingUrl(); the
  return query is success=1 / canceled=1, which the billing page reads.
  The billing page highlights ?tier=pro|pro_plus, and signing in from a
  billing link returns to the same plan.
- auth/callback pins the redirect origin in production and rejects
  protocol-relative next= values (open redirect).
- Mobile legal links use SITE_URLS (fixes the missing slash on /terms).
- Compose drops the unused NEXT_PUBLIC_API_URL and the dead wwwroot legal
  mounts; deploy scripts add the web image and the SUPABASE_* values the NAS
  compose already required; .dockerignore keeps app .env files out of images.
- Supabase auth redirects allow /app/** (remote dashboard must match).

Policy: docs/REFACTOR_POLICY.md Wave 3, W3-3 and W3-4.

apps/desktop/tests/unit/license-open-billing.spec.ts

@@ -0,0 +1,50 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+import { app, ipcMain, shell } from 'electron'
+import { IPC_CHANNELS } from '@d3ro/core/ipc-channels'
+
+vi.mock('../../src/main/services/LicenseService', () => ({
+  getLicenseService: () => ({ on: vi.fn() })
+}))
+
+import { registerLicenseHandlers } from '../../src/main/ipc/license-handlers'
+
+type CapturedHandler = (...args: unknown[]) => unknown
+
+const handlers = new Map<string, CapturedHandler>()
+
+async function openBilling(tier: 'pro' | 'pro_plus'): Promise<unknown> {
+  const handler = handlers.get(IPC_CHANNELS.LICENSE.OPEN_BILLING)
+  if (!handler) throw new Error('Missing OPEN_BILLING handler')
+  return handler({}, { tier })
+}
+
+function setPackaged(value: boolean): void {
+  Object.defineProperty(app, 'isPackaged', { value, configurable: true, writable: true })
+}
+
+beforeEach(() => {
+  vi.clearAllMocks()
+  handlers.clear()
+  vi.mocked(ipcMain.handle).mockImplementation((channel: string, handler: CapturedHandler) => {
+    handlers.set(channel, handler)
+  })
+  registerLicenseHandlers()
+})
+
+describe('LICENSE.OPEN_BILLING', () => {
+  it('opens the single web billing entry with the chosen tier in packaged builds', async () => {
+    setPackaged(true)
+    try {
+      await expect(openBilling('pro_plus')).resolves.toEqual({ success: true, data: undefined })
+      expect(shell.openExternal).toHaveBeenCalledWith('https://d3ro.chanpaca.net/app/billing?tier=pro_plus')
+    } finally {
+      setPackaged(false)
+    }
+  })
+
+  it('opens the local web app under the same base path in development', async () => {
+    setPackaged(false)
+    await openBilling('pro')
+    expect(shell.openExternal).toHaveBeenCalledWith('http://localhost:3000/app/billing?tier=pro')
+  })
+})