style(templates): format Selmer .html templates for readability

Many templates were minified onto a single line. Reformatted every template under
resources/templates/ with djLint (django profile, 2-space indent) so the markup,
{% %} blocks, and {{ }} interpolations are human-readable, plus hand-split the two
multi-<span> option partials (invoice-option / rule-option). Pure reflow — no markup,
tag, or text content changed (the only content-adjacent delta is harmless trailing
whitespace inside single-interpolation elements). link.html / panel-empty.html stay on
one line (single element). resources/public/index.html left as-is (already readable,
non-template static).

Full e2e suite 72/72 green (no rendering regressions).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

resources/templates/components/button-group.html

@@ -1 +1,6 @@
-<div class="inline-flex rounded-md shadow-sm" role="group" hx-on:click="this.querySelector(&quot;input&quot;).value = event.target.value; this.querySelector(&quot;input&quot;).dispatchEvent(new Event('change', {bubbles: true}));"><input type="hidden" name="{{ name }}">{{ body|safe }}</div>
+<div class="inline-flex rounded-md shadow-sm"
+     role="group"
+     hx-on:click="this.querySelector(&quot;input&quot;).value = event.target.value; this.querySelector(&quot;input&quot;).dispatchEvent(new Event('change', {bubbles: true}));">
+  <input type="hidden" name="{{ name }}">
+  {{ body|safe }}
+</div>