feat: add modular services and repositories for improved code organization

Introduce repository pattern across multiple services, including `favorites`, `tags`, `sessions`, `reports`, `auth`, and more. Decouple crypto functionalities into modular services like `HashingService`, `JwtService`, and `EncryptionService`. Improve testability and maintainability by simplifying dependencies and consolidating utility logic.

backend/src/crypto/services/hashing.service.ts

@@ -0,0 +1,32 @@
+import { Injectable } from "@nestjs/common";
+import { hash, verify } from "@node-rs/argon2";
+
+@Injectable()
+export class HashingService {
+	async hashEmail(email: string): Promise<string> {
+		const normalizedEmail = email.toLowerCase().trim();
+		return this.hashSha256(normalizedEmail);
+	}
+
+	async hashIp(ip: string): Promise<string> {
+		return this.hashSha256(ip);
+	}
+
+	async hashSha256(text: string): Promise<string> {
+		const data = new TextEncoder().encode(text);
+		const hashBuffer = await crypto.subtle.digest("SHA-256", data);
+		return Array.from(new Uint8Array(hashBuffer))
+			.map((b) => b.toString(16).padStart(2, "0"))
+			.join("");
+	}
+
+	async hashPassword(password: string): Promise<string> {
+		return hash(password, {
+			algorithm: 2,
+		});
+	}
+
+	async verifyPassword(password: string, hash: string): Promise<boolean> {
+		return verify(hash, password);
+	}
+}