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/event_embed.html

@@ -7,7 +7,7 @@
 {% endblock %}
 
 {% block content %}
-         <span class="float-right">
+         <span class="float-end">
             {% if object.mic %}
             <div class="text-center">
                 <img src="{{ object.mic.profile_picture }}" class="event-mic-photo rounded"/>
@@ -39,8 +39,8 @@
             </small>
         </h3>
         {% include 'partials/event_status.html' %}
-        <div class="row ml-2">
-            <div class="col-xs-6 pr-2">
+        <div class="row ms-2">
+            <div class="col-6 pe-2">
                 <p>
                     {% if object.is_rig %}
                     <strong>Client:</strong> {{ object.person.name }}
@@ -61,7 +61,7 @@
                     {% endif %}
                 </p>
             </div>
-            <div class="col-xs-6 px-2">
+            <div class="col-6 px-2">
                 {% if object.meet_at %}
                 <p>
                     <strong>Crew meet:</strong>