feat(documents): detail page with signers, watchers, activity, actions

Replaces the PR4 stub at /documents/[id] with the full Phase A detail
view: gradient header strip, status-aware action bar (Cancel /
Download / Email signatories), per-signer remind + copy-link, watcher
list with remove, and activity timeline. Adds the supporting endpoints
(cancel, compose-completion-email, watchers GET/POST/DELETE) and
listDocumentWatchers / addDocumentWatcher / removeDocumentWatcher
service helpers. The document GET now serves the aggregator shape
when ?detail=true.

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

src/lib/services/documents.service.ts

@@ -1095,6 +1095,69 @@ export async function composeSignedDocEmail(
   };
 }
 
+// ─── Watchers (PR5) ───────────────────────────────────────────────────────────
+
+export async function listDocumentWatchers(documentId: string, portId: string) {
+  await getDocumentById(documentId, portId); // port-scope check
+  return db
+    .select({
+      userId: documentWatchers.userId,
+      addedBy: documentWatchers.addedBy,
+      addedAt: documentWatchers.addedAt,
+    })
+    .from(documentWatchers)
+    .where(eq(documentWatchers.documentId, documentId));
+}
+
+export async function addDocumentWatcher(
+  documentId: string,
+  portId: string,
+  userId: string,
+  meta: AuditMeta,
+): Promise<{ userId: string; addedAt: Date }> {
+  await getDocumentById(documentId, portId);
+  const [row] = await db
+    .insert(documentWatchers)
+    .values({ documentId, userId, addedBy: meta.userId })
+    .onConflictDoNothing()
+    .returning();
+  void createAuditLog({
+    userId: meta.userId,
+    portId,
+    action: 'create',
+    entityType: 'document_watcher',
+    entityId: documentId,
+    newValue: { documentId, watcherUserId: userId },
+    ipAddress: meta.ipAddress,
+    userAgent: meta.userAgent,
+  });
+  emitToRoom(`port:${portId}`, 'document:updated', { documentId });
+  return row ? { userId: row.userId, addedAt: row.addedAt } : { userId, addedAt: new Date() };
+}
+
+export async function removeDocumentWatcher(
+  documentId: string,
+  portId: string,
+  userId: string,
+  meta: AuditMeta,
+): Promise<void> {
+  await getDocumentById(documentId, portId);
+  await db
+    .delete(documentWatchers)
+    .where(and(eq(documentWatchers.documentId, documentId), eq(documentWatchers.userId, userId)));
+  void createAuditLog({
+    userId: meta.userId,
+    portId,
+    action: 'delete',
+    entityType: 'document_watcher',
+    entityId: documentId,
+    oldValue: { documentId, watcherUserId: userId },
+    ipAddress: meta.ipAddress,
+    userAgent: meta.userAgent,
+  });
+  emitToRoom(`port:${portId}`, 'document:updated', { documentId });
+}
+
 /**
  * Skeleton for the create-document wizard entry point (PR6).
  *