feat(externally-signed): mark contract/reservation as signed without file

Step 4 second slice. Adds the "Mark as signed without file" action to
contract + reservation tabs per PRE-DEPLOY-PLAN § 1.5.14.

Service: `markExternallySigned(interestId, portId, docType, reason)`
flips the relevant doc-status column ('contract_doc_status' /
'reservation_doc_status' / 'eoi_doc_status') to 'signed', writes an
audit log entry with `metadata.type='externally_signed'` capturing
the optional reason, and fires the appropriate berth-rule trigger
(eoi_signed / contract_signed) so downstream automation (berth
status flips, notifications) treats it identically to a Documenso-
signed completion.

Route: POST /api/v1/interests/[id]/mark-externally-signed gated on
interests.edit. Validates docType against the canonical 3-value enum.

UI: <MarkExternallySignedDialog> AlertDialog with optional reason
textarea + per-docType copy. Wired into EmptyContractState and
EmptyReservationState empty-state buttons. The action sits alongside
"Upload draft for signing" and "Upload paper-signed copy" as a third
option for reps whose canonical paper lives elsewhere.

EOI not yet wired into a UI surface — the eoi flow already has a
full upload pipeline. Service supports it for completeness.

Followup: quick brochure/PDF download buttons + per-user reminder
digest schedule still pending in Step 4 backlog.

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

src/app/api/v1/interests/[id]/mark-externally-signed/route.ts

@@ -0,0 +1,47 @@
+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, NotFoundError } from '@/lib/errors';
+import { markExternallySigned } from '@/lib/services/external-signing.service';
+
+const bodySchema = z.object({
+  docType: z.enum(['eoi', 'reservation', 'contract']),
+  reason: z.string().trim().max(2000).optional(),
+});
+
+/**
+ * POST /api/v1/interests/[id]/mark-externally-signed
+ *
+ * Marks the named document type as signed without requiring a file
+ * upload. Sets the relevant `*_doc_status` column to 'signed', writes
+ * an audit log entry capturing the reason, and fires the appropriate
+ * berth-rule trigger (eoi_signed / contract_signed) if any.
+ */
+export const POST = withAuth(
+  withPermission('interests', 'edit', async (req, ctx, params) => {
+    try {
+      const interestId = params.id;
+      if (!interestId) throw new NotFoundError('Interest');
+      const input = await parseBody(req, bodySchema);
+      const result = await markExternallySigned(
+        {
+          interestId,
+          portId: ctx.portId,
+          docType: input.docType,
+          reason: input.reason ?? null,
+        },
+        {
+          userId: ctx.userId,
+          portId: ctx.portId,
+          ipAddress: ctx.ipAddress,
+          userAgent: ctx.userAgent,
+        },
+      );
+      return NextResponse.json({ data: result });
+    } catch (error) {
+      return errorResponse(error);
+    }
+  }),
+);