feat(branding): multi-tenant brand naming + per-port email shell + auth UI continuity

Removes the last hardcoded "Port Nimara" references so a tenant cloning
the deploy with a fresh slug sees their own brand throughout.

Browser + native chrome:
- `generateMetadata` reads `branding_app_name` from the first port row
  so the browser tab title, apple-web-app title, and template literal
  reflect the tenant (fallback "CRM" until DB is seeded).
- Mobile topbar derives the brand-mark initials from the port slug
  ("port-nimara" → "PN", "marina-alpha" → "MA") — no code edit on clone.
- `documenso-payload` default redirect URL is `""` so Documenso falls
  back to its own post-sign page instead of routing every tenant's
  signers to portnimara.com; per-port `redirectUrl` setting still wins.
- Server-startup log uses generic "CRM server listening".

Email + auth shell:
- New `auth-shell-branding.ts` resolves logo / background / appName once
  per request from `system_settings`; used by both the email shell and
  the auth-pages SSR layout.
- `auth-branding-provider` wraps `/login`, `/reset-password`, `/set-password`,
  portal `/portal/*` so the branded shell hydrates with the same assets
  the inbox sees.
- `me/email` change email uses the branded shell instead of inline HTML
  with "Port Nimara CRM" baked into copy.
- Admin branding page adds an email-preview card (POSTs to
  `/api/v1/admin/branding/email-preview`) so an admin can spot-check
  their templates before going live.
- `/api/public/files/[id]` exposes branding-category files anonymously
  so inbox images (no session cookie) can render; any other category
  still flows through authenticated `/api/v1/files/[id]/preview`.

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

tests/unit/services/documenso-payload.test.ts

@@ -250,9 +250,13 @@ describe('buildDocumensoPayload', () => {
     expect(payload.meta.message).toContain('On behalf of Blue Seas');
   });
 
-  it('uses default redirect URL when not provided', () => {
+  it('uses empty default redirect URL when not provided (Documenso falls back to its own page)', () => {
+    // Multi-tenant: never hardcode a single port's marketing-site URL
+    // here. When the admin hasn't configured a redirect, send empty
+    // string so Documenso uses its built-in post-sign page. Per-port
+    // override flows through getPortDocumensoConfig → redirectUrl.
     const payload = buildDocumensoPayload(makeContext(), OPTIONS);
-    expect(payload.meta.redirectUrl).toBe('https://portnimara.com');
+    expect(payload.meta.redirectUrl).toBe('');
   });
 
   it('uses custom redirect URL when provided', () => {