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

templates/base_embed.html

@@ -11,6 +11,7 @@
 
     <meta name="color-scheme" content="light dark">
 
+    {% include 'partials/dark_theme.html' %}
     <link rel="stylesheet" type="text/css" href="{% static 'css/screen.css' %}">
 </head>
 
@@ -20,8 +21,7 @@
         {% if messages %}
             {% for message in messages %}
                 <div class="alert alert-{{ message.level_tag }} alert-dismissible" role="alert">
-                    <button type="button" class="close" data-dismiss="alert" aria-label="Close"><span
-                            aria-hidden="true">&times;</span></button>
+                    <button type="button" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>
                     {{ message }}
                 </div>
             {% endfor %}
@@ -31,7 +31,6 @@
         {% endblock %}
     </div>
 </div>
-{% include 'partials/dark_theme.html' %}
 {% block js %}
 {% endblock %}
 </body>