Refactor CSS architecture per css-methodology-spec.md

Split CSS into named layers: reset → colors → typography → base →
components → utilities. Each component has one unique root class in
its own file. No cross-component overrides.

New files:
- reset.css (modern-normalize base — matches project's prior reset)
- colors.css (all colour variables)
- typography.css (font faces, size/space scale, font-family vars)
- base.css (≤ 5 site-wide rules: layout, headings)
- utilities.css (sr-only, skip-link, reduced-motion)
- style.css (root @import file loading all layers)
- components/{links,focus,forms,tables,dialog,details,media,
  buttons,badges,toasts,pagination,header,search}.css

Existing files:
- variables.css → backward-compat wrapper (imports colors + typography)
- common.css → backward-compat wrapper (imports style.css)
- Page files (admin, public, form, tfe, apropos, repertoire, system,
  file-access) → removed redundant @import url(./variables.css)
- head.php → loads style.css instead of modern-normalize + common.css
- partage pages → load style.css

Fixes vs initial refactoring:
- reset.css: use modern-normalize base (not Tailwind Preflight) to
  avoid border/list/heading regressions from aggressive defaults
- components/search.css: restore !important flags on input styles
  (needed to override forms.css base input selectors)
- acces.php: add toast feedback on password copy button

Cleaned up duplicate status-badge/toast definitions from admin.css
(now live in components/badges.css and components/toast.css).

app/public/assets/css/components/search.css

@@ -0,0 +1,43 @@
+/* ============================================================
+   SEARCH BAR — Shared header search form
+   Root class: .header-search-wrap
+   ============================================================ */
+
+.header-search-wrap {
+  padding: 0;
+  flex-shrink: 0;
+  background: linear-gradient(180deg, var(--gradient-4) 0%, #ffffffee 100%);
+}
+
+.header-search-form { width: 100%; }
+
+.header-search-input-wrap {
+  position: relative;
+  display: flex;
+  align-items: center;
+}
+
+.header-search-icon {
+  position: absolute;
+  left: var(--space-s);
+  width: 18px;
+  height: 18px;
+  stroke: var(--accent-primary);
+  pointer-events: none;
+}
+
+.header-search-input-wrap input {
+  width: 100%;
+  padding: var(--space-2xs) var(--space-s) !important;
+  padding-left: calc(18px + var(--space-l)) !important;
+  border: 1px solid var(--accent-primary) !important;
+  border-radius: var(--radius) !important;
+  background: var(--bg-primary) !important;
+  font-size: var(--step-0) !important;
+  color: var(--text-primary) !important;
+  font-family: inherit !important;
+}
+
+.header-search-input-wrap input::placeholder {
+  color: var(--accent-primary) !important;
+}