feat: enable CSP in all environments (local/preview/prod) (QuivrHQ#1334)

# Description

Enable CSP in all environments (local/preview/prod).

Relies on NEXT_PUBLIC_ENV env variable, which should be
`'local'|'preview'|'prod'`

# Comparison of old and new CSP values (tested locally)

## Before

### CSP (for prod only)

```
default-src 'self' https://fonts.googleapis.com https://xxx.supabase.co https://api.june.so https://www.quivr.app/; connect-src 'self' https://xxx.supabase.co http://localhost:5050 https://api.june.so https://api.openai.com https://cdn.growthbook.io https://vitals.vercel-insights.com/v1/vitals; img-src 'self' https://www.gravatar.com data:; media-src 'self' https://user-images.githubusercontent.com https://www.quivr.app/ https://quivr-cms.s3.eu-west-3.amazonaws.com; script-src 'unsafe-inline' 'unsafe-eval' https://va.vercel-scripts.com/ https://www.quivr.app/ https://www.google-analytics.com/; frame-ancestors 'none'; style-src 'unsafe-inline' https://www.quivr.app/;
```

## After

### Prod CSP (iso with before)

```
default-src 'self' https://fonts.googleapis.com https://xxx.supabase.co https://api.june.so https://www.quivr.app/; connect-src 'self' https://xxx.supabase.co http://localhost:5050 https://api.june.so https://api.openai.com https://cdn.growthbook.io https://vitals.vercel-insights.com/v1/vitals; img-src 'self' https://www.gravatar.com data:; media-src 'self' https://user-images.githubusercontent.com https://www.quivr.app/ https://quivr-cms.s3.eu-west-3.amazonaws.com; script-src 'unsafe-inline' 'unsafe-eval' https://va.vercel-scripts.com/ https://www.quivr.app/ https://www.google-analytics.com/; frame-ancestors 'none'; style-src 'unsafe-inline' https://www.quivr.app/;
```

### Preview CSP

```
default-src 'self' https://fonts.googleapis.com https://xxx.supabase.co https://api.june.so https://preview.quivr.app/; connect-src 'self' https://xxx.supabase.co http://localhost:5050 https://api.june.so https://api.openai.com https://cdn.growthbook.io https://vitals.vercel-insights.com/v1/vitals; img-src 'self' https://www.gravatar.com data:; media-src 'self' https://user-images.githubusercontent.com https://www.quivr.app/ https://quivr-cms.s3.eu-west-3.amazonaws.com; script-src 'unsafe-inline' 'unsafe-eval' https://va.vercel-scripts.com/ https://preview.quivr.app/ https://www.google-analytics.com/; frame-ancestors 'none'; style-src 'unsafe-inline' https://preview.quivr.app/;
```

### Local CSP

```
default-src 'self' https://fonts.googleapis.com https://xxx.supabase.co https://api.june.so http://localhost:3000 http://localhost:3001; connect-src 'self' https://xxx.supabase.co http://localhost:5050 https://api.june.so https://api.openai.com https://cdn.growthbook.io https://vitals.vercel-insights.com/v1/vitals; img-src 'self' https://www.gravatar.com data:; media-src 'self' https://user-images.githubusercontent.com https://www.quivr.app/ https://quivr-cms.s3.eu-west-3.amazonaws.com; script-src 'unsafe-inline' 'unsafe-eval' https://va.vercel-scripts.com/ http://localhost:3000 http://localhost:3001 https://www.google-analytics.com/; frame-ancestors 'none'; style-src 'unsafe-inline' http://localhost:3000 http://localhost:3001;
```

# 🧪 External checks

Syntax checked with https://csp-evaluator.withgoogle.com/ (for the 3
environments).

---------

Co-authored-by: gozineb <zinebe@theodo.fr>

frontend/next.config.js

@@ -9,16 +9,12 @@ const nextConfig = {
   },
   // eslint-disable-next-line prefer-arrow/prefer-arrow-functions
   async headers() {
-    if (process.env.NEXT_PUBLIC_ENV === "prod") {
-      return [
-        {
-          source: "/(.*)",
-          headers: securityHeaders,
-        },
-      ];
-    } else {
-      return [];
-    }
+    return [
+      {
+        source: "/(.*)",
+        headers: securityHeaders,
+      },
+    ];
   },
 };
 
@@ -28,7 +24,11 @@ const ContentSecurityPolicy = {
     "https://fonts.googleapis.com",
     process.env.NEXT_PUBLIC_SUPABASE_URL,
     "https://api.june.so",
-    "https://www.quivr.app/",
+    {
+      prod: "https://www.quivr.app/",
+      preview: "https://preview.quivr.app/",
+      local: ["http://localhost:3000", "http://localhost:3001"],
+    },
   ],
   "connect-src": [
     "'self'",
@@ -50,13 +50,38 @@ const ContentSecurityPolicy = {
     "'unsafe-inline'",
     "'unsafe-eval'",
     "https://va.vercel-scripts.com/",
-    "https://www.quivr.app/",
+    {
+      prod: "https://www.quivr.app/",
+      preview: "https://preview.quivr.app/",
+      local: ["http://localhost:3000", "http://localhost:3001"],
+    },
     "https://www.google-analytics.com/",
   ],
   "frame-ancestors": ["'none'"],
-  "style-src": ["'unsafe-inline'", "https://www.quivr.app/"],
+  "style-src": [
+    "'unsafe-inline'",
+    {
+      prod: "https://www.quivr.app/",
+      preview: "https://preview.quivr.app/",
+      local: ["http://localhost:3000", "http://localhost:3001"],
+    },
+  ],
 };
 
+// Resolve environment-specific CSP values
+for (const directive of Object.values(ContentSecurityPolicy)) {
+  for (const [index, resource] of directive.entries()) {
+    if (typeof resource === "string") {
+      continue;
+    }
+    directive[index] = resource[process.env.NEXT_PUBLIC_ENV];
+    if (Array.isArray(directive[index])) {
+      directive[index] = directive[index].join(" ");
+    }
+  }
+}
+
+// Build CSP string
 const cspString = Object.entries(ContentSecurityPolicy)
   .map(([key, values]) => `${key} ${values.join(" ")};`)
   .join(" ");