frontend: Add Wireframes and Mockups

CONTRIBUTING.md

@@ -113,6 +113,27 @@ Registration (`POST /auth/register`) is handled by `AuthController` and
 `RegistrationService` (server-side bean validation plus duplicate
 username/email detection).
 
+#### Design: Mockups and Wireframes
+
+The frontend look and feel is specified before code:
+
+- **[Figma file](https://www.figma.com/design/2q1Rt5NGbQ1w8gRtRGoF4A)**
+  (read-only): low-fidelity wireframes (page structure) and high-fidelity
+  mockups (Catppuccin theme).
+- **[Browsable HTML mockups](docs/design/mockups/index.html)**: the same
+  pages as static HTML/CSS; their markup and BEM classes are the blueprint
+  for the future Thymeleaf templates.
+- **[docs/design/theme-exploration.md](docs/design/theme-exploration.md)**:
+  the design tokens and their WCAG contrast ratios;
+  [mockups-explained.md](docs/design/mockups-explained.md)
+  (FR: [mockups-explained-fr.md](docs/design/mockups-explained-fr.md)) and
+  the per-file docs in [docs/design/mockups/](docs/design/mockups/) explain
+  every tag and CSS rule.
+
+Frontend contributions are expected to follow the mockups, consume colors
+only through the design tokens, and use the BEM naming convention (see
+[Code Style and Formatting](#code-style-and-formatting)).
+
 #### MonoRepo
 
 We use a **monorepo**, that is a Git repository containing mainly both the **frontend and** the **backend**.

README.md

@@ -379,6 +379,12 @@ visit [this link](https://github.com/users/ebouchut/projects/7/views/3).
 - [GLOSSARY.md](GLOSSARY.md) — definitions of the domain and technical terms used across the project
   (🇫🇷 French version: [GLOSSAIRE.md](GLOSSAIRE.md)).
 - [Architecture Decision Records](docs/adr/README.md) — A list of design decisions and their trade-offs.
+- [Mockups and wireframes (Figma)](https://www.figma.com/design/2q1Rt5NGbQ1w8gRtRGoF4A) —
+  read-only Figma file with the high-fidelity mockups (Catppuccin theme) and the
+  low-fidelity wireframes of the frontend pages; the browsable HTML mockups and
+  their study docs live in [docs/design/](docs/design/theme-exploration.md)
+  (see [mockups-explained.md](docs/design/mockups-explained.md),
+  🇫🇷 [mockups-explained-fr.md](docs/design/mockups-explained-fr.md)).
 - [Test coverage (Codecov)](https://app.codecov.io/gh/ebouchut/learn-dev) —
   live coverage dashboard fed by CI
   (see [ADR-0012](docs/adr/0012-publish-test-coverage-to-codecov.md));