Add comprehensive thesis management system with database migration

This commit introduces a complete thesis management interface and migrates
the system from YAML-based storage to SQLite:

Core Changes:
- Add Database.php helper class with PDO connection and entity management
- Add list.php for viewing all theses with filtering and sorting
- Add edit.php for modifying existing thesis records
- Add import.php for migrating legacy YAML data to SQLite
- Add justfile with development tasks (serve, init-test-db, etc.)

Documentation:
- Add MIGRATION.md with complete migration guide and architecture docs
- Update README.md with database setup and Just recipe instructions
- Update .gitignore to exclude test databases and error logs

Modified Forms:
- Enhanced formulaire.php with transaction-based SQLite processing
- Updated index.php with database-driven form options
- Improved thanks.php to read from database views

The new architecture provides:
- Normalized database schema (19 tables, 2 views)
- Transaction safety and referential integrity
- CRUD operations for thesis management
- Filtering by year, orientation, AP program, publication status
- Secure file handling with metadata tracking

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

front-backend/Database.php

@@ -0,0 +1,111 @@
+<?php
+
+/**
+ * Database connection class for SQLite
+ */
+class Database {
+    private static $instance = null;
+    private $pdo;
+
+    /**
+     * Private constructor to prevent multiple instances
+     */
+    private function __construct() {
+        $dbPath = __DIR__ . '/../formulaire/test.db';
+
+        if (!file_exists($dbPath)) {
+            throw new Exception("Database file not found: " . $dbPath);
+        }
+
+        try {
+            $this->pdo = new PDO('sqlite:' . $dbPath);
+            $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
+            $this->pdo->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
+        } catch (PDOException $e) {
+            error_log("Database connection failed: " . $e->getMessage());
+            throw $e;
+        }
+    }
+
+    /**
+     * Get singleton instance
+     */
+    public static function getInstance() {
+        if (self::$instance === null) {
+            self::$instance = new self();
+        }
+        return self::$instance;
+    }
+
+    /**
+     * Get PDO connection
+     */
+    public function getConnection() {
+        return $this->pdo;
+    }
+
+    /**
+     * Get all published theses with pagination
+     */
+    public function getPublishedTheses($limit = 10, $offset = 0) {
+        $sql = "SELECT * FROM v_theses_public ORDER BY year DESC, title ASC LIMIT :limit OFFSET :offset";
+        $stmt = $this->pdo->prepare($sql);
+        $stmt->bindValue(':limit', $limit, PDO::PARAM_INT);
+        $stmt->bindValue(':offset', $offset, PDO::PARAM_INT);
+        $stmt->execute();
+        return $stmt->fetchAll();
+    }
+
+    /**
+     * Count all published theses
+     */
+    public function countPublishedTheses() {
+        $sql = "SELECT COUNT(*) as count FROM theses WHERE is_published = 1";
+        $stmt = $this->pdo->query($sql);
+        $result = $stmt->fetch();
+        return $result['count'];
+    }
+
+    /**
+     * Get thesis by ID with all related data
+     */
+    public function getThesisById($id) {
+        $sql = "SELECT * FROM v_theses_full WHERE id = :id AND is_published = 1";
+        $stmt = $this->pdo->prepare($sql);
+        $stmt->bindValue(':id', $id, PDO::PARAM_INT);
+        $stmt->execute();
+        $thesis = $stmt->fetch();
+
+        if (!$thesis) {
+            return null;
+        }
+
+        // Get associated files
+        $thesis['files'] = $this->getThesisFiles($id);
+
+        return $thesis;
+    }
+
+    /**
+     * Get files associated with a thesis
+     */
+    public function getThesisFiles($thesisId) {
+        $sql = "SELECT * FROM thesis_files WHERE thesis_id = :thesis_id ORDER BY file_type, uploaded_at";
+        $stmt = $this->pdo->prepare($sql);
+        $stmt->bindValue(':thesis_id', $thesisId, PDO::PARAM_INT);
+        $stmt->execute();
+        return $stmt->fetchAll();
+    }
+
+    /**
+     * Prevent cloning
+     */
+    private function __clone() {}
+
+    /**
+     * Prevent unserialization
+     */
+    public function __wakeup() {
+        throw new Exception("Cannot unserialize singleton");
+    }
+}