feat: enhance Stripstream configuration handling

- Introduced a new resolver function to streamline fetching Stripstream configuration from the database or environment variables.
- Updated various components and API routes to utilize the new configuration resolver, improving code maintainability and reducing direct database calls.
- Added optional environment variables for Stripstream URL and token in the .env.example file.
- Refactored image loading logic in the reader components to improve performance and error handling.

src/app/api/stripstream/images/books/[bookId]/pages/[pageNumber]/route.ts

@@ -1,7 +1,7 @@
 import type { NextRequest } from "next/server";
 import { NextResponse } from "next/server";
 import { getCurrentUser } from "@/lib/auth-utils";
-import prisma from "@/lib/prisma";
+import { getResolvedStripstreamConfig } from "@/lib/providers/stripstream/stripstream-config-resolver";
 import { StripstreamClient } from "@/lib/providers/stripstream/stripstream.client";
 import { ERROR_CODES } from "@/constants/errorCodes";
 import { AppError } from "@/utils/errors";
@@ -23,7 +23,7 @@ export async function GET(
     }
 
     const userId = parseInt(user.id, 10);
-    const config = await prisma.stripstreamConfig.findUnique({ where: { userId } });
+    const config = await getResolvedStripstreamConfig(userId);
     if (!config) {
       throw new AppError(ERROR_CODES.STRIPSTREAM.MISSING_CONFIG);
     }

src/app/api/stripstream/images/books/[bookId]/thumbnail/route.ts

@@ -1,7 +1,7 @@
 import type { NextRequest } from "next/server";
 import { NextResponse } from "next/server";
 import { getCurrentUser } from "@/lib/auth-utils";
-import prisma from "@/lib/prisma";
+import { getResolvedStripstreamConfig } from "@/lib/providers/stripstream/stripstream-config-resolver";
 import { StripstreamClient } from "@/lib/providers/stripstream/stripstream.client";
 import { AppError } from "@/utils/errors";
 import { ERROR_CODES } from "@/constants/errorCodes";
@@ -20,7 +20,7 @@ export async function GET(
     }
 
     const userId = parseInt(user.id, 10);
-    const config = await prisma.stripstreamConfig.findUnique({ where: { userId } });
+    const config = await getResolvedStripstreamConfig(userId);
     if (!config) {
       throw new AppError(ERROR_CODES.STRIPSTREAM.MISSING_CONFIG);
     }