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/reset.css

@@ -0,0 +1,104 @@
+/* ============================================================
+   RESET — Based on modern-normalize v3.0.1 (what this project
+   originally used). Do not modify this file.
+   ============================================================ */
+
+*, ::before, ::after {
+  box-sizing: border-box;
+}
+
+html {
+  font-family: system-ui, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji';
+  line-height: 1.15;
+  -webkit-text-size-adjust: 100%;
+  tab-size: 4;
+}
+
+body {
+  margin: 0;
+}
+
+b, strong {
+  font-weight: bolder;
+}
+
+code, kbd, pre, samp {
+  font-family: ui-monospace, SFMono-Regular, Consolas, 'Liberation Mono', Menlo, monospace;
+  font-size: 1em;
+}
+
+small {
+  font-size: 80%;
+}
+
+sub, sup {
+  font-size: 75%;
+  line-height: 0;
+  position: relative;
+  vertical-align: baseline;
+}
+
+sub { bottom: -0.25em; }
+sup { top: -0.5em; }
+
+table {
+  border-color: currentcolor;
+}
+
+button, input, optgroup, select, textarea {
+  font-family: inherit;
+  font-size: 100%;
+  line-height: 1.15;
+  margin: 0;
+}
+
+[type=button], [type=reset], [type=submit], button {
+  -webkit-appearance: button;
+}
+
+legend {
+  padding: 0;
+}
+
+progress {
+  vertical-align: baseline;
+}
+
+::-webkit-inner-spin-button,
+::-webkit-outer-spin-button {
+  height: auto;
+}
+
+[type=search] {
+  -webkit-appearance: textfield;
+  outline-offset: -2px;
+}
+
+::-webkit-search-decoration {
+  -webkit-appearance: none;
+}
+
+::-webkit-file-upload-button {
+  -webkit-appearance: button;
+  font: inherit;
+}
+
+summary {
+  display: list-item;
+}
+
+/* Additional minimal resets not in modern-normalize */
+
+img, svg, video, canvas, audio, iframe, embed, object {
+  display: block;
+  vertical-align: middle;
+}
+
+img, video {
+  max-width: 100%;
+  height: auto;
+}
+
+[hidden] {
+  display: none;
+}