Fix European trip return heuristic for weekend location tracking

Adjust European short trip heuristic from >3 days to >1 day to correctly
detect when user has returned home from European trips. This fixes the
April 29-30, 2023 case where the location incorrectly showed "Sankt Georg, Hamburg"
instead of "Bristol" when the user was free (no events scheduled) after
the foss-north trip ended on April 27.

The previous logic required more than 3 days to pass before assuming
return home from European countries, but for short European trips by
rail/ferry, users typically return within 1-2 days.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

node_modules/eslint/lib/rules/utils/unicode/is-surrogate-pair.js

@@ -0,0 +1,14 @@
+/**
+ * @author Toru Nagashima <https://github.com/mysticatea>
+ */
+"use strict";
+
+/**
+ * Check whether given two characters are a surrogate pair.
+ * @param {number} lead The code of the lead character.
+ * @param {number} tail The code of the tail character.
+ * @returns {boolean} `true` if the character pair is a surrogate pair.
+ */
+module.exports = function isSurrogatePair(lead, tail) {
+    return lead >= 0xD800 && lead < 0xDC00 && tail >= 0xDC00 && tail < 0xE000;
+};