css: moved + tweaked styles to common.css

- Add baseline input[type="checkbox"] and input[type="radio"] styling
  in common.css (accent-color, size, cursor, flex-shrink)
- Give select a solid background (var(--bg-primary)) and its own focus rule
- Remove now-redundant checkbox accent-color/size from
  .admin-checkbox-label (form.css) and .param-checkbox (admin.css)
- Simplify .search-filter-select (repertoire.css) to inherit common
  select defaults (border, background, arrow icon)
- Keep all layout-specific classes in form.css and admin.css intact
- Add baseline input[type="checkbox"] and input[type="radio"] styling
  in common.css (accent-color, size, cursor, flex-shrink)
- Give select its own rule block with same shape as text inputs
  (transparent background, same padding/border/radius/focus)
- Remove now-redundant checkbox accent-color/size from
  .admin-checkbox-label (form.css) and .param-checkbox (admin.css)
- Simplify .search-filter-select (repertoire.css) to inherit common
  select defaults
- Keep all layout-specific classes in form.css and admin.css intact
- Remove bottom-border/border-radius:0 overrides from .admin-form,
  .admin-inline-form, .param-form, and .param-grid inputs/selects
- Change required-field indicator from border-bottom-style to
  border-style: dashed to work with full-border approach
- Update param-grid aria-invalid from border-bottom-color to border-color
- All text inputs, selects, and textareas now inherit the full-border
  style from common.css (border, border-radius, padding, focus ring)
- .password-gate input[password]: remove redundant padding override
- .retry-email-form input[email]: remove redundant border/border-radius/
  padding/box-sizing, keep only font-size (larger) and width
- .tfe-access-request-form input/textarea: remove broken references to
  undefined vars (--border, --background, --accent), now inherit from
  common.css. Remove redundant focus rule.
- .fhb-name-input: strip redundant padding/border/radius/font-size/font
- .admin-inline-form input/select: strip redundant font-size
- .param-checkbox: remove font-size (inherits from body)
- .param-checkbox small: remove redundant color + font-size (common.css small already sets both)
- .param-note: remove font-size
- .param-account-status: remove font-size
- .param-smtp-test-row label: remove display:block + font-size (common.css label)
- .param-smtp-status: remove font-size
- .param-grid label: remove font-size
- Remove .param-form legend padding override (now inherits common.css legend)
- Remove .param-danger-zone legend padding override
- Remove .param-export-zone legend padding override
- Remove .param-fieldset-inline legend entirely (only rule was padding)
- Remove .licence-explanation legend entirely (all properties identical to common.css legend)
- All fieldsets now consistently use common.css fieldset padding
  (0 var(--space-m) var(--space-m) var(--space-m))
- The common.css fieldset has padding-top: 0, which leaves checkboxes
  and other content tight against the legend. Add var(--space-s) top
  padding so the first content row has proper spacing from the legend.

app/public/assets/css/common.css

@@ -411,12 +411,13 @@ label {
   margin-bottom: var(--space-3xs);
 }
 
+/* ── Text inputs, selects, textareas ─────────────────────────────── */
+
 input:not([type="checkbox"]):not([type="radio"]):not([type="file"]):not(
   [type="hidden"]
 ):not([type="submit"]):not([type="button"]):not([type="reset"]):not(
   [type="color"]
 ),
-select,
 textarea {
   font-family: inherit;
   font-size: var(--step--1);
@@ -433,7 +434,6 @@ input:not([type="checkbox"]):not([type="radio"]):not([type="file"]):not(
 ):not([type="submit"]):not([type="button"]):not([type="reset"]):not(
   [type="color"]
 ):focus,
-select:focus,
 textarea:focus {
   outline: none;
   border: 2px solid var(--accent-primary);
@@ -451,14 +451,45 @@ textarea {
   line-height: 1.5;
 }
 
+/* ── Select ──────────────────────────────────────────────────────── */
+
 select {
+  font-family: inherit;
+  font-size: var(--step--1);
+  padding: var(--space-2xs) var(--space-xs);
+  padding-right: 1.75rem;
+  border: 1px solid var(--border-primary);
+  border-radius: var(--radius);
+  background: transparent;
+  color: var(--text-primary);
   cursor: pointer;
   background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='8' viewBox='0 0 12 8'%3E%3Cpath d='M1 1l5 5 5-5' stroke='%23999' stroke-width='1.5' fill='none' stroke-linecap='round'/%3E%3C/svg%3E");
   background-repeat: no-repeat;
-  background-position: right 0.5rem center;
-  padding-right: 1.5rem;
+  background-position: right 0.55rem center;
   -webkit-appearance: none;
   appearance: none;
+  transition: border-color 0.15s;
+}
+
+select:focus {
+  outline: none;
+  border: 2px solid var(--accent-primary);
+}
+
+/* ── Checkboxes & radios ─────────────────────────────────────────── */
+
+input[type="checkbox"],
+input[type="radio"] {
+  accent-color: var(--accent-primary);
+  width: 16px;
+  height: 16px;
+  cursor: pointer;
+  flex-shrink: 0;
+  margin: 0;
+}
+
+input[type="radio"] {
+  border-radius: 50%;
 }
 
 /* ============================================================