feat: implement group-based access control (Admin, Standard_User, Leadership, Read_Only)

- Add user_group migration and created_by column migration
- Replace requireRole middleware with requireGroup
- Update all backend routes to use group-based authorization
- Add Standard_User conditional delete with ownership, state, and compliance checks
- Add cascade impact check for CVE deletes
- Update AuthContext with group-based permission helpers
- Update all frontend components for group-based rendering
- Update UserManagement UI with group dropdown, confirmation dialogs, self-demotion prevention

backend/migrations/add_created_by_columns.js

@@ -0,0 +1,76 @@
+// Migration: Add created_by column to cves, archer_tickets, and jira_tickets tables
+// Stores the user ID of the creator for ownership-based delete checks.
+// Idempotent — safe to run multiple times.
+const sqlite3 = require('sqlite3').verbose();
+const path = require('path');
+
+/**
+ * Run the migration against the given database instance.
+ * Exported for testing with in-memory databases.
+ * @param {sqlite3.Database} db
+ * @returns {Promise<void>}
+ */
+function runMigration(db) {
+    return new Promise((resolve, reject) => {
+        const tables = ['cves', 'archer_tickets', 'jira_tickets'];
+        let completed = 0;
+
+        db.serialize(() => {
+            tables.forEach((table) => {
+                db.all(`PRAGMA table_info(${table})`, (err, columns) => {
+                    if (err) {
+                        // Table may not exist yet — skip gracefully
+                        console.log(`⚠ Could not inspect ${table}: ${err.message} — skipping`);
+                        completed++;
+                        if (completed === tables.length) resolve();
+                        return;
+                    }
+
+                    const hasCreatedBy = columns.some(col => col.name === 'created_by');
+
+                    if (hasCreatedBy) {
+                        console.log(`✓ ${table}.created_by already exists — skipping`);
+                        completed++;
+                        if (completed === tables.length) resolve();
+                        return;
+                    }
+
+                    db.run(
+                        `ALTER TABLE ${table} ADD COLUMN created_by INTEGER REFERENCES users(id)`,
+                        (err) => {
+                            if (err) {
+                                reject(err);
+                                return;
+                            }
+                            console.log(`✓ Added created_by column to ${table}`);
+                            completed++;
+                            if (completed === tables.length) resolve();
+                        }
+                    );
+                });
+            });
+        });
+    });
+}
+
+// Run directly if executed as a script
+if (require.main === module) {
+    const dbPath = path.join(__dirname, '..', 'cve_database.db');
+    const db = new sqlite3.Database(dbPath);
+    console.log('Starting add_created_by_columns migration...');
+
+    runMigration(db)
+        .then(() => {
+            console.log('Migration complete!');
+            db.close(() => {
+                console.log('Database connection closed.');
+            });
+        })
+        .catch((err) => {
+            console.error('Migration failed:', err);
+            db.close();
+            process.exit(1);
+        });
+}
+
+module.exports = { runMigration };