feat: garden calendar + lists integrations (task 74)

- calendar-bridge.ts and lists-bridge.ts isolate cross-module deps
- scheduleOnCalendar action: creates event from care schedule with 30-min
  slot, title convention (Water/Fertilize/Repot/Prune/custom), reminder opt
- pushOverdueToTaskList action: inserts one task per overdue (plant+schedule)
  pair into the default task list, skips duplicate text entries
- CareScheduleEditor: per-row calendar 📅 button opens inline form with
  calendar select + optional reminder minutes + success link to /calendar
- Garden page header: PushOverdueButton with auto-dismissing feedback toast

src/modules/garden/components/push-overdue-button.tsx

@@ -0,0 +1,47 @@
+"use client";
+
+import { useEffect, useState, useTransition } from "react";
+import { pushOverdueToTaskList } from "../server/actions";
+
+export function PushOverdueButton() {
+  const [message, setMessage] = useState<string | null>(null);
+  const [isError, setIsError] = useState(false);
+  const [isPending, startTransition] = useTransition();
+
+  useEffect(() => {
+    if (!message) return;
+    const id = setTimeout(() => setMessage(null), 4000);
+    return () => clearTimeout(id);
+  }, [message]);
+
+  function handleClick() {
+    setMessage(null);
+    setIsError(false);
+    startTransition(async () => {
+      try {
+        const { added } = await pushOverdueToTaskList();
+        setMessage(
+          added === 0
+            ? "No overdue care tasks."
+            : `Added ${added} task${added !== 1 ? "s" : ""} to your task list.`,
+        );
+      } catch {
+        setIsError(true);
+        setMessage("Failed to push tasks. Please try again.");
+      }
+    });
+  }
+
+  return (
+    <div className="flex items-center gap-2">
+      <button onClick={handleClick} disabled={isPending} className="btn btn-ghost btn-sm">
+        {isPending ? "Pushing…" : "Add overdue to task list"}
+      </button>
+      {message && (
+        <span className={`text-xs ${isError ? "text-red-500" : "text-[var(--ink-mute)]"}`}>
+          {message}
+        </span>
+      )}
+    </div>
+  );
+}