feat: theme config service — REST API with versioning + backup

- ThemeService: read/write/validate theme.json, auto-backup on save
- ThemeController: GET/PUT/POST /api/config/theme (public GET, versioned PUT)
- ThemeConfig type with version + updatedAt fields
- Default theme: Global Hospital blue scale
- ConfigThemeModule registered in AppModule

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/config/theme.defaults.ts

@@ -0,0 +1,79 @@
+export type ThemeConfig = {
+    version?: number;
+    updatedAt?: string;
+    brand: {
+        name: string;
+        hospitalName: string;
+        logo: string;
+        favicon: string;
+    };
+    colors: {
+        brand: Record<string, string>;
+    };
+    typography: {
+        body: string;
+        display: string;
+    };
+    login: {
+        title: string;
+        subtitle: string;
+        showGoogleSignIn: boolean;
+        showForgotPassword: boolean;
+        poweredBy: { label: string; url: string };
+    };
+    sidebar: {
+        title: string;
+        subtitle: string;
+    };
+    ai: {
+        quickActions: Array<{ label: string; prompt: string }>;
+    };
+};
+
+export const DEFAULT_THEME: ThemeConfig = {
+    brand: {
+        name: 'Helix Engage',
+        hospitalName: 'Global Hospital',
+        logo: '/helix-logo.png',
+        favicon: '/favicon.ico',
+    },
+    colors: {
+        brand: {
+            '25': 'rgb(239 246 255)',
+            '50': 'rgb(219 234 254)',
+            '100': 'rgb(191 219 254)',
+            '200': 'rgb(147 197 253)',
+            '300': 'rgb(96 165 250)',
+            '400': 'rgb(59 130 246)',
+            '500': 'rgb(37 99 235)',
+            '600': 'rgb(29 78 216)',
+            '700': 'rgb(30 64 175)',
+            '800': 'rgb(30 58 138)',
+            '900': 'rgb(23 37 84)',
+            '950': 'rgb(15 23 42)',
+        },
+    },
+    typography: {
+        body: "'Satoshi', var(--font-inter, 'Inter'), -apple-system, 'Segoe UI', Roboto, Arial, sans-serif",
+        display: "'General Sans', var(--font-inter, 'Inter'), -apple-system, 'Segoe UI', Roboto, Arial, sans-serif",
+    },
+    login: {
+        title: 'Sign in to Helix Engage',
+        subtitle: 'Global Hospital',
+        showGoogleSignIn: true,
+        showForgotPassword: true,
+        poweredBy: { label: 'Powered by F0rty2.ai', url: 'https://f0rty2.ai' },
+    },
+    sidebar: {
+        title: 'Helix Engage',
+        subtitle: 'Global Hospital \u00b7 {role}',
+    },
+    ai: {
+        quickActions: [
+            { label: 'Doctor availability', prompt: 'What doctors are available and what are their visiting hours?' },
+            { label: 'Clinic timings', prompt: 'What are the clinic locations and timings?' },
+            { label: 'Patient history', prompt: "Can you summarize this patient's history?" },
+            { label: 'Treatment packages', prompt: 'What treatment packages are available?' },
+        ],
+    },
+};