Bootstrap 5 & remove jQuery (#661)

* build: move frontend assets to Bootstrap 5.3 and Tom Select

* feat: migrate templates and scripts to Bootstrap 5, dropping jQuery

Templates
- Rename Bootstrap 4 classes and data attributes (data-bs-*, ms-/me-/ps-/pe-,
  text-start/end, form-group -> mb-3, input-group wrappers removed, badges,
  custom controls -> form-check/form-select, media -> d-flex, btn-close, ...)
- Dark mode now uses Bootstrap 5.3 colour modes (data-bs-theme on <html>),
  set from <head> to avoid a flash of the light theme
- Remove the Bootstrap 4 /bootstrap/ demo page
- Contextual table classes (table-success etc.) still work as plain
  backgrounds for the rigboard key

JavaScript
- Remove jQuery: src.js/interaction.js and every inline template script are
  rewritten in plain JS on top of small helpers (helpers.js, bundled with
  Bootstrap into jpop.js so inline scripts can use them)
- Replace bootstrap-select/ajax-bootstrap-select with Tom Select. The remote
  search now sends the `q` parameter and reads `text`, which is what the
  API actually uses (the old picker sent `term` and read `label`)
- HTML fragments are fetched with an X-Requested-With header so views keep
  rendering their modal variants, and fetched scripts are re-executed
- Remove the Bootstrap 4 plugin script includes

* fix: stop rigboard header buttons stretching to full width under Bootstrap 5

* fix: restore dark-mode brand colours and contextual table colours under Bootstrap 5

* fix: brighten dark-mode links and make coloured card outlines visible

* fix: calendar layout and grid borders, navbar search button width, guard missing modal links

* fix: readable text in dark-mode Tom Select inputs and placeholders, restore form-control column widths

* build: split the Dockerfile into cached stages with prod and dev targets

* deploy: make compose.yml development-only with live reload, and document it

* fix: keep badge text colour for links inside badges

* fix: restore table-bordered grid lines in dark mode

* fix: include Bootstrap's progress styles and keep progress labels readable

RIGS/templates/invoice_dashboard.html

@@ -4,8 +4,8 @@
 {% block content %}
 
 <form method="GET" action="{% url 'invoice_dashboard' %}">
-    <div class="form-row">
-        <div class="form-group col-md-4">
+    <div class="row g-2">
+        <div class="mb-3 col-md-4">
             <label for="time_filter">Time Filter</label>
             <select id="time_filter" name="time_filter" class="form-control">
                 <option value="week" {% if time_filter == 'week' %}selected{% endif %}>Last Week (7 days)</option>
@@ -18,8 +18,8 @@
 </form>
 
 <script>
-    $('#time_filter').change(function () {
-        $(this).closest('form').submit();
+    document.getElementById('time_filter').addEventListener('change', function () {
+        this.closest('form').submit();
     });
 </script>
 
@@ -27,7 +27,7 @@
 
 <!-- big cards in 2x2 grid with total_outstanding, total_events, total_invoices and total_payments, different backgrounds -->
 
-<div class="card-deck">
+<div class="row row-cols-1 row-cols-md-4 g-3">
     <div class="card">
         <a href="{% url 'invoice_waiting' %}" class="text-decoration-none text-white">
             <div class="card-body bg-primary">