Add schedule sync and schedule-aware playback

src/timezone_helper.h

@@ -22,6 +22,11 @@ const std::vector<CountryTimeZones>& getStandardTimeZones();
 // Converts a UTC timestamp to the user's configured IANA timezone
 std::string formatUtcToTimezone(time_t utc_time, const std::string& iana_code, const std::string& format = "%Y-%m-%d %H:%M:%S %Z");
 
+// Wall-clock minutes since midnight (0-1439) right now in `iana_code`. Used by
+// the schedule to pick the active listening block. Falls back to UTC when the
+// timezone is empty.
+int currentLocalMinutes(const std::string& iana_code);
+
 // Gets current UTC timestamp as ISO string
 std::string getUtcTimestampIso();