fix(js): replace synchronous AJAX call in reservation.js with async pattern

[JohnVillalovos]

Analysis by Claude Code.

Problem

Web/scripts/reservation.js:862-870 uses async: false in a $.ajax() call within the getLayoutItems() function. This blocks the browser's main thread while fetching schedule layout data, freezing the entire UI until the request completes (or times out).

Synchronous XMLHttpRequest on the main thread is deprecated by all major browsers and Chrome already shows console warnings for it.

Current code

var getLayoutItems = function (scheduleId, date) {
  // ...cache check...
  $.ajax({
    url: 'schedule.php',
    dataType: 'json',
    data: { dr: 'layout', sid: scheduleId, ld: date },
    success: function (data) {
      layoutCache[weekday] = data.periods;
    },
    async: false,
  });
  return layoutCache[weekday];
};

The reason async: false is used is so the function can return the result synchronously. Two callers depend on this:

• PopulatePeriodDropDown() (line ~899) — uses the return value to populate period <select> dropdowns
• previousDateEndsAtMidnight() (line ~847) — calls getLayoutItems() for its side effect on layoutCache, then reads the cache

Proposed fix

Convert getLayoutItems() to return a Promise (or use a callback), and make its callers async-aware:

1. Change getLayoutItems() to return a $.ajax() Promise (just remove async: false and return the jqXHR)
2. Update PopulatePeriodDropDown() to use .done() / .then() to populate the dropdown after the response arrives
3. Update previousDateEndsAtMidnight() similarly, chaining the result
4. Keep the layoutCache optimization — when the cache hits, resolve immediately without a network call

Acceptance criteria

• No async: false in the codebase
• Period dropdowns still populate correctly when changing reservation dates
• Layout cache still works (no redundant requests for the same weekday)
• No visible UI regression on the reservation page

[labmecanicatec]

It seems the proposal is on the right track; the only thing I can suggest is disabling <select> until it loads