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>

src/app/api/v1/admin/branding/email-preview/route.ts

@@ -0,0 +1,86 @@
+import { NextResponse } from 'next/server';
+import { z } from 'zod';
+
+import { withAuth, withPermission } from '@/lib/api/helpers';
+import { errorResponse, ValidationError } from '@/lib/errors';
+import { parseBody } from '@/lib/api/route-helpers';
+import { getPortBrandingConfig } from '@/lib/services/port-config';
+import { renderShell } from '@/lib/email/shell';
+import { sendEmail } from '@/lib/email';
+
+const SAMPLE_SUBJECT_SUFFIX = ' — branding preview';
+
+function buildSampleEmail(branding: {
+  logoUrl: string | null;
+  emailBackgroundUrl: string | null;
+  primaryColor: string;
+  appName: string;
+  emailHeaderHtml: string | null;
+  emailFooterHtml: string | null;
+}): { subject: string; html: string } {
+  const subject = `${branding.appName}${SAMPLE_SUBJECT_SUFFIX}`;
+  const body = `
+    <h1 style="font-size:20px;margin:0 0 12px;color:${branding.primaryColor};">A sample notification</h1>
+    <p style="margin:0 0 12px;color:#334155;">Hi there,</p>
+    <p style="margin:0 0 12px;color:#334155;">
+      This is a preview of how transactional emails from <strong>${branding.appName}</strong>
+      will look using the current branding settings (logo, background image, primary color,
+      and any custom header/footer HTML you've added).
+    </p>
+    <p style="margin:0 0 12px;">
+      <a href="https://example.com" style="display:inline-block;padding:10px 18px;background-color:${branding.primaryColor};color:#ffffff;text-decoration:none;border-radius:6px;font-weight:600;">
+        Primary action button
+      </a>
+    </p>
+    <p style="margin:0;color:#64748b;font-size:13px;">
+      Adjust the values in the Identity and Email branding cards above, save, then refresh the
+      preview to see your changes.
+    </p>
+  `;
+  const html = renderShell({
+    title: subject,
+    body,
+    branding: {
+      logoUrl: branding.logoUrl,
+      backgroundUrl: branding.emailBackgroundUrl,
+      primaryColor: branding.primaryColor,
+      emailHeaderHtml: branding.emailHeaderHtml,
+      emailFooterHtml: branding.emailFooterHtml,
+    },
+  });
+  return { subject, html };
+}
+
+// GET — return the sample email rendered with the current port's branding.
+export const GET = withAuth(
+  withPermission('admin', 'manage_settings', async (_req, ctx) => {
+    try {
+      if (!ctx.portId) throw new ValidationError('No active port');
+      const branding = await getPortBrandingConfig(ctx.portId);
+      const { subject, html } = buildSampleEmail(branding);
+      return NextResponse.json({ data: { subject, html } });
+    } catch (error) {
+      return errorResponse(error);
+    }
+  }),
+);
+
+const sendTestSchema = z.object({
+  recipient: z.string().email('Enter a valid email address'),
+});
+
+// POST — actually send the sample email to a single recipient.
+export const POST = withAuth(
+  withPermission('admin', 'manage_settings', async (req, ctx) => {
+    try {
+      if (!ctx.portId) throw new ValidationError('No active port');
+      const { recipient } = await parseBody(req, sendTestSchema);
+      const branding = await getPortBrandingConfig(ctx.portId);
+      const { subject, html } = buildSampleEmail(branding);
+      await sendEmail(recipient, subject, html);
+      return NextResponse.json({ data: { sent: true, recipient } });
+    } catch (error) {
+      return errorResponse(error);
+    }
+  }),
+);