Implement share viewer (task 31)

- Makes actorId nullable in activity_log (migration 0010) with onDelete:
  set null so audit history survives user deletion; adds logShareActivity
  for anonymous mutations
- Adds resolveShareToken return of householdId for downstream validation
- Adds renderSharedView to EntityTypeRegistration; each module implements
  loadForShare (no-session bare queries) and renderSharedView
- Calendar: CalendarSharedView (upcoming 90-day events) and
  EventSharedView (title/time/location/notes)
- Lists: ListSharedView (client component with optimistic toggles via
  toggleShareListItem server action in lists/server/share-actions.ts)
- Notes: NoteSharedView (title + body + updated date)
- /app/s/[token]/page.tsx: resolves token, dispatches to loadForShare +
  renderSharedView, friendly error for invalid/expired tokens, noindex
- Middleware /s/* exemption confirmed present (no change needed)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/s/[token]/page.tsx

@@ -0,0 +1,50 @@
+import type { Metadata } from "next";
+import { resolveShareToken } from "@/modules/_core/share";
+import { getEntityType } from "@/modules/_core/registry";
+
+export const metadata: Metadata = {
+  robots: { index: false, follow: false },
+};
+
+export default async function SharePage({
+  params,
+}: {
+  params: Promise<{ token: string }>;
+}) {
+  const { token } = await params;
+
+  const resolved = await resolveShareToken(token);
+  if (!resolved) return <ShareError />;
+
+  const entityReg = getEntityType(resolved.entityType);
+  if (!entityReg?.loadForShare || !entityReg.renderSharedView) {
+    return <ShareError message="This content type cannot be shared." />;
+  }
+
+  const data = await entityReg.loadForShare(resolved.entityId);
+  if (!data) return <ShareError />;
+
+  return (
+    <div className="min-h-screen">
+      <div className="border-b bg-background px-4 py-3">
+        <p className="text-xs text-muted-foreground">
+          Shared via famapp
+          {resolved.capabilities.write ? " · You can edit this" : " · View only"}
+        </p>
+      </div>
+      {entityReg.renderSharedView({ data, capabilities: resolved.capabilities, token })}
+    </div>
+  );
+}
+
+function ShareError({ message }: { message?: string }) {
+  return (
+    <div className="flex min-h-[60vh] flex-col items-center justify-center gap-3 p-8 text-center">
+      <h1 className="text-xl font-semibold">Link not found</h1>
+      <p className="max-w-sm text-sm text-muted-foreground">
+        {message ??
+          "This share link may have expired or been revoked. Ask the sender for a new link."}
+      </p>
+    </div>
+  );
+}