feat(invoices): remove client-facing PDF generation

Phase 1 / commit 11 of 14 — invoices are client-facing documents, and
per the new "no CRM-generated client-facing PDFs" rule (see the design
spec), the in-app pdfme rendering is removed entirely.

Future invoice rendering will use the deferred AcroForm-fill admin-
template feature: admin uploads a PDF template with named form fields,
CRM fills them with invoice data via pdf-lib. Same pattern as the
in-app EOI pathway. Tracked in BACKLOG.md.

Deleted:
  - src/lib/services/invoices.ts:generateInvoicePdf (60 LOC)
  - src/lib/pdf/templates/invoice-template.ts (entire pdfme template)
  - src/app/api/v1/invoices/[id]/generate-pdf/route.ts
  - src/components/invoices/invoice-pdf-preview.tsx (regenerate UI)
  - "PDF Preview" tab on invoice detail page
  - 5 now-unused imports in invoices.ts (files, ports, buildStoragePath,
    getStorageBackend, env)

sendInvoice() retained: still queues the send-invoice email job, still
flips status to "sent", still emits the socket event. The PDF-attach
step is gone — downstream consumers either render externally or wait
for the AcroForm-fill feature. The `pdfFileId` column on invoices stays
so existing rows don't break, just never gets written by this code path.

1319/1319 vitest green.

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

src/app/api/v1/invoices/[id]/generate-pdf/route.ts

@@ -1,21 +0,0 @@
-import { NextResponse } from 'next/server';
-
-import { withAuth, withPermission } from '@/lib/api/helpers';
-import { errorResponse } from '@/lib/errors';
-import { generateInvoicePdf } from '@/lib/services/invoices';
-
-export const POST = withAuth(
-  withPermission('invoices', 'edit', async (_req, ctx, params) => {
-    try {
-      const fileRecord = await generateInvoicePdf(params.id!, ctx.portId, {
-        userId: ctx.userId,
-        portId: ctx.portId,
-        ipAddress: ctx.ipAddress,
-        userAgent: ctx.userAgent,
-      });
-      return NextResponse.json({ data: fileRecord });
-    } catch (error) {
-      return errorResponse(error);
-    }
-  }),
-);