feat(email-routing): per-category send-from routing infra + admin matrix

Per PRE-DEPLOY-PLAN § 1.3.7. Lays the foundation for admin-configurable
routing of every outbound email category to either the noreply or
sales sender account.

Pieces shipped:
- `src/lib/services/email-routing.ts` — EmailCategory enum (17
  categories covering every shipped surface), DEFAULT_CATEGORY_ROUTING
  map (auth/notifications/EOI-invite → noreply; brochure/PDF/sales
  send-outs → sales), `resolveSenderForCategory()` + a graceful
  fallback to noreply when the resolved sender is sales but creds
  aren't configured.
- `GET / PATCH /api/v1/admin/email/routing` endpoints — gated on
  `admin.manage_settings`. Returns the routing + sales-availability
  flag + canonical category list.
- `EmailRoutingCard` — matrix UI dropped into /admin/email below the
  sales-email-config card. Per-category dropdown auto-disables the
  `sales` option when the port has no sales SMTP creds; explains the
  state in an amber callout. Save-on-change with toast + "Reset to
  defaults" button.

Setting persisted as `system_settings.email_routing` (JSONB blob).
Followup: opportunistic migration of existing dispatchers (sendEmail,
createSalesTransporter callers) to use `resolveSenderForCategory()` —
the defaults preserve current behavior so this is non-blocking.

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

src/app/api/v1/admin/email/routing/route.ts

@@ -0,0 +1,50 @@
+import { NextResponse } from 'next/server';
+import { z } from 'zod';
+
+import { withAuth, withPermission } from '@/lib/api/helpers';
+import { parseBody } from '@/lib/api/route-helpers';
+import { errorResponse } from '@/lib/errors';
+import { upsertSetting } from '@/lib/services/settings.service';
+import {
+  EMAIL_CATEGORIES,
+  EMAIL_ROUTING_KEY,
+  getEmailRoutingMatrix,
+} from '@/lib/services/email-routing';
+
+const senderSchema = z.enum(['noreply', 'sales']);
+const updateSchema = z.object({
+  routing: z.record(z.enum(EMAIL_CATEGORIES), senderSchema),
+});
+
+export const GET = withAuth(
+  withPermission('admin', 'manage_settings', async (_req, ctx) => {
+    try {
+      const matrix = await getEmailRoutingMatrix(ctx.portId);
+      return NextResponse.json({
+        data: { ...matrix, categories: EMAIL_CATEGORIES },
+      });
+    } catch (error) {
+      return errorResponse(error);
+    }
+  }),
+);
+
+export const PATCH = withAuth(
+  withPermission('admin', 'manage_settings', async (req, ctx) => {
+    try {
+      const input = await parseBody(req, updateSchema);
+      await upsertSetting(EMAIL_ROUTING_KEY, input.routing, ctx.portId, {
+        userId: ctx.userId,
+        portId: ctx.portId,
+        ipAddress: ctx.ipAddress,
+        userAgent: ctx.userAgent,
+      });
+      const matrix = await getEmailRoutingMatrix(ctx.portId);
+      return NextResponse.json({
+        data: { ...matrix, categories: EMAIL_CATEGORIES },
+      });
+    } catch (error) {
+      return errorResponse(error);
+    }
+  }),
+);