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>

data/theme-backups/theme-2026-04-02T09-43-19-186Z.json

@@ -0,0 +1,62 @@
+{
+  "brand": {
+    "name": "Helix Engage",
+    "hospitalName": "Global Hospital",
+    "logo": "/helix-logo.png",
+    "favicon": "/favicon.ico"
+  },
+  "colors": {
+    "brand": {
+      "25": "rgb(248 250 252)",
+      "50": "rgb(241 245 249)",
+      "100": "rgb(226 232 240)",
+      "200": "rgb(203 213 225)",
+      "300": "rgb(148 163 184)",
+      "400": "rgb(100 116 139)",
+      "500": "rgb(71 85 105)",
+      "600": "rgb(47 64 89)",
+      "700": "rgb(37 49 72)",
+      "800": "rgb(30 41 59)",
+      "900": "rgb(15 23 42)",
+      "950": "rgb(2 6 23)"
+    }
+  },
+  "typography": {
+    "body": "'Plus Jakarta Sans', 'Inter', sans-serif",
+    "display": "'Plus Jakarta Sans', 'Inter', sans-serif"
+  },
+  "login": {
+    "title": "Sign in to Ramaiah",
+    "subtitle": "Ramaiah Hospital",
+    "showGoogleSignIn": true,
+    "showForgotPassword": true,
+    "poweredBy": {
+      "label": "Powered by F0rty2.ai",
+      "url": "https://f0rty2.ai"
+    }
+  },
+  "sidebar": {
+    "title": "Ramaiah",
+    "subtitle": "Ramaiah Hospital · {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?"
+      }
+    ]
+  }
+}