feat(reminders): cadence-aware framework with auto/manual modes

isReminderDue now keys off doc.remindersDisabled and the effective
cadence (per-doc override → template default), dropping the implicit
interests.reminderEnabled gate so non-EOI docs auto-remind correctly.
sendReminderIfAllowed gains an options bag — auto:true keeps the 9-16
window + cadence cooldown for the cron, auto:false bypasses both for
manual UI sends. signerId targets a specific pending signer (must be
next in sequential mode). 7 unit tests cover the cadence math.

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

src/app/api/v1/documents/[id]/remind/route.ts

@@ -1,14 +1,30 @@
 import { NextResponse } from 'next/server';
+import { z } from 'zod';
 
 import { withAuth, withPermission } from '@/lib/api/helpers';
 import { errorResponse } from '@/lib/errors';
 import { sendReminderIfAllowed } from '@/lib/services/document-reminders';
 
+const remindBodySchema = z
+  .object({
+    signerId: z.string().optional(),
+  })
+  .optional();
+
 export const POST = withAuth(
   withPermission('documents', 'edit', async (req, ctx, params) => {
     try {
-      const sent = await sendReminderIfAllowed(params.id!, ctx.portId);
-      return NextResponse.json({ data: { sent } });
+      let signerId: string | undefined;
+      const text = await req.text();
+      if (text) {
+        const parsed = remindBodySchema.safeParse(JSON.parse(text));
+        if (parsed.success && parsed.data) signerId = parsed.data.signerId;
+      }
+      const result = await sendReminderIfAllowed(params.id!, ctx.portId, {
+        auto: false,
+        signerId,
+      });
+      return NextResponse.json({ data: result });
     } catch (error) {
       return errorResponse(error);
     }