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/partials/legacy_event_table.html

@@ -94,7 +94,7 @@
 }
 </style>
 <div id="event_table">
-    <div class="eventgrid grid-header font-weight-bold">
+    <div class="eventgrid grid-header fw-bold">
         <div id="event_number">#</div>
         <div id="event_dates">Dates & Times</div>
         <div>Event Details</div>
@@ -117,29 +117,29 @@
     table-warning
     {% endif %}" {% if event.cancelled %}style="opacity: 50% !important;"{% endif %} id="event_row">
     <!---Number-->
-    <div class="font-weight-bold c-none c-lg-block" id="event_number">{{ event.display_id }}</div>
+    <div class="fw-bold c-none c-lg-block" id="event_number">{{ event.display_id }}</div>
     <!--Dates & Times-->
     <div id="event_dates" style="min-width: 180px;">
         <dl>
           {% if not event.cancelled %}
             {% if event.meet_at %}
-            <dt class="font-weight-normal">Meet:</dt>
-            <dd class="text-nowrap font-weight-bold text-lg-right">{{ event.meet_at|date:"D d/m/Y H:i" }}</dd>
+            <dt class="fw-normal">Meet:</dt>
+            <dd class="text-nowrap fw-bold text-lg-right">{{ event.meet_at|date:"D d/m/Y H:i" }}</dd>
             {% endif %}
             {% if event.access_at %}
-            <dt class="font-weight-normal">Access:</dt>
-            <dd class="text-nowrap font-weight-bold text-lg-right">{{ event.access_at|date:"D d/m/Y H:i" }}</dd>
+            <dt class="fw-normal">Access:</dt>
+            <dd class="text-nowrap fw-bold text-lg-right">{{ event.access_at|date:"D d/m/Y H:i" }}</dd>
             {% endif %}
           {% endif %}
-          <dt class="font-weight-normal">Start:</dt>
-          <dd class="text-nowrap font-weight-bold text-lg-right">{{ event.start_date|date:"D d/m/Y" }}
+          <dt class="fw-normal">Start:</dt>
+          <dd class="text-nowrap fw-bold text-lg-right">{{ event.start_date|date:"D d/m/Y" }}
             {% if event.has_start_time %}
               {{ event.start_time|date:"H:i" }}
             {% endif %}
           </dd>
           {% if event.end_date %}
-          <dt class="font-weight-normal">End:</dt>
-          <dd class="text-nowrap font-weight-bold text-lg-right">{{ event.end_date|date:"D d/m/Y" }}
+          <dt class="fw-normal">End:</dt>
+          <dd class="text-nowrap fw-bold text-lg-right">{{ event.end_date|date:"D d/m/Y" }}
             {% if event.has_end_time %}
             {{ event.end_time|date:"H:i" }}
             {% endif %}
@@ -154,7 +154,7 @@
                 <span class="c-inline c-lg-none">{{ event }}</span><span class="c-none c-lg-inline">{{ event.name }}</span>
             </a>
             {% if event.dry_hire %}
-            <span class="badge badge-secondary">Dry Hire</span>
+            <span class="badge text-bg-secondary">Dry Hire</span>
             {% endif %}
             <br class="c-none c-lg-inline">
             {% if event.venue %}