Add License slide to introduction

Briefly describe the EUPL-1.2 licence, the inbound = outbound contribution
rule, and the practical consequences for users (rights, obligations,
warranty disclaimer).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/sections/intro.tex

@@ -284,3 +284,47 @@ report:
   \item \href{https://git.beafrancois.fr/v-and-v/testium/src/branch/main/test/validation}{ \tum{testium} validation suite}
 \end{itemize}
 \end{frame}
+
+% ===== License =====
+\subsection{License}
+
+\begin{frame}{\tum{testium} license}
+\begin{columns}
+  \column{0.5\textwidth}
+    \begin{itemize}
+      \item Distributed under the \textbf{EUPL-1.2}
+      \begin{itemize}
+        \item European Union Public Licence v1.2
+        \item Open-source, OSI / FSF approved
+        \item Governed by the law of the licensor's EU country (France)
+      \end{itemize}
+      \item SPDX identifier: \incode{EUPL-1.2}
+      \item Files in the repository:
+      \begin{itemize}
+        \item \incode{LICENSE} (full legal text)
+        \item \incode{CONTRIBUTING.md} (contribution rules)
+      \end{itemize}
+      \item Contributions follow the \emph{inbound = outbound} rule
+      \begin{itemize}
+        \item Any patch you submit is licensed under the same EUPL-1.2
+        \item No CLA, no copyright assignment
+      \end{itemize}
+    \end{itemize}
+  \column{0.5\textwidth}
+    \begin{itemize}
+      \item \textbf{You may}:
+      \begin{itemize}
+        \item Use \tum{testium} for any purpose, including commercial
+        \item Read, modify, redistribute the source code
+        \item Combine with code under GPL, AGPL, LGPL, MPL, CeCILL, EPL\ldots (compatibility appendix)
+      \end{itemize}
+      \item \textbf{You must}:
+      \begin{itemize}
+        \item Keep the copyright and license notices
+        \item Redistribute modified versions under the EUPL (or a compatible license)
+        \item Publish your modifications even when offering \tum{testium} as a network service (SaaS clause)
+      \end{itemize}
+      \item \textbf{No warranty}, no liability of the author
+    \end{itemize}
+\end{columns}
+\end{frame}