Add security standards and CI infrastructure

- SECURITY.md with vulnerability disclosure policy and self-hosting guidance
- Dependabot config for weekly dependency updates (npm, Docker, Actions)
- ESLint v9 flat config for frontend and backend, with eslint-plugin-security
- GitHub Actions CI: lint, typecheck, build, and npm audit on every push/PR
- CodeQL workflow for automated security scanning (runs on push and weekly)

frontend/eslint.config.js

@@ -0,0 +1,33 @@
+import js from '@eslint/js';
+import tseslint from 'typescript-eslint';
+import reactPlugin from 'eslint-plugin-react';
+import reactHooks from 'eslint-plugin-react-hooks';
+import security from 'eslint-plugin-security';
+
+export default tseslint.config(
+  { ignores: ['dist/**', 'node_modules/**'] },
+  js.configs.recommended,
+  ...tseslint.configs.recommended,
+  security.configs.recommended,
+  {
+    files: ['src/**/*.{ts,tsx}'],
+    plugins: {
+      react: reactPlugin,
+      'react-hooks': reactHooks,
+    },
+    rules: {
+      // React rules
+      ...reactPlugin.configs.recommended.rules,
+      ...reactHooks.configs.recommended.rules,
+      'react/react-in-jsx-scope': 'off', // Not needed with React 17+ JSX transform
+      'react/prop-types': 'off',         // TypeScript handles this
+
+      // TypeScript rules
+      '@typescript-eslint/no-explicit-any': 'warn',
+      '@typescript-eslint/no-unused-vars': ['warn', { argsIgnorePattern: '^_' }],
+    },
+    settings: {
+      react: { version: 'detect' },
+    },
+  }
+);