form: add spacing between elements inside fieldsets

- common.css: fieldset > *:not(:last-child) gets margin-bottom: var(--space-xs)
- admin.css: .param-form fieldset > * zeroes margin to avoid double-spacing with flex gap

TODO.md

@@ -105,6 +105,10 @@
 - [x] Fix single-valued FK columns (years, ap, or, fi): matched entries now use full intersection so clicking one entry correctly fades others with zero results
 - [x] Fix column ordering: students between finalité and mots-clés
 
+## Add spacing between form elements inside fieldsets
+- [x] `common.css` — `fieldset > *:not(:last-child) { margin-bottom: var(--space-xs); }`
+- [x] `admin.css` — `.param-form fieldset > * { margin-bottom: 0; }` to avoid double-spacing with flex gap
+
 ## Standardise buttons with .btn base class
 - [x] Create `.btn` base class in common.css: `border-radius: 10px; padding: var(--space-xs)` + background + cursor
 - [x] Add `.btn--primary` (accent bg), `.btn--secondary` (--bg bg + border), `.btn--sm`, `.btn--lg`, `.btn--danger`, `.btn--warning`, `.btn--success`, `.btn--ghost`, `.btn--muted`, `.btn--blue`, `.btn--yellow`, `.btn--green`, `.btn--red` modifiers

app/public/assets/css/admin.css

@@ -904,6 +904,10 @@
     gap: var(--space-xs);
 }
 
+.param-form fieldset > * {
+    margin-bottom: 0;
+}
+
 .param-form legend {
     padding: 0 var(--space-xs);
 }

app/public/assets/css/common.css

@@ -571,6 +571,10 @@ fieldset {
     margin: 0;
 }
 
+fieldset > *:not(:last-child) {
+    margin-bottom: var(--space-xs);
+}
+
 legend {
     font-size: var(--step--1);
     font-weight: 600;