Add architecture section and diagram to README

Added architecture section with a detailed diagram illustrating the system components and their interactions.

Author: noobdevsam

README.md

@@ -10,6 +10,8 @@ This project is a powerful and secure steganography tool built with Spring Boot
 
 - [What is Steganography?](#what-is-steganography)
 - [Features](#features)
+- [Architecture](#architecture)
+- [Demo](#demo)
 - [Docker Hub](#docker-hub)
 - [How It Works](#how-it-works)
   - [Encoding Process](#encoding-process)
@@ -50,6 +52,80 @@ Steganography is the practice of concealing a message or file within another fil
 - **Robust Error Handling**: A global exception handler provides detailed, structured error responses (`ProblemDetail`) for API clients.
 - **Traceability**: A `CorrelationIdFilter` adds a unique trace ID to every request for improved logging and debugging.
 
+## Architecture
+
+```mermaid
+graph TD
+    subgraph "User / Client"
+        User[<fa:fa-user> User/API Client]
+    end
+
+    subgraph "DevOps & CI/CD Pipeline"
+        GH_Repo[<fa:fa-github> GitHub Repo] -->|Push to master<br>New Release| GH_Actions[<fa:fa-cogs> GitHub Actions<br>Build, Test, & Publish]
+        GH_Actions -->|Publishes Image| DockerHub[<fa:fa-docker> Docker Hub<br>noobdevsam/spring-project-steganography-tool]
+    end
+
+    subgraph "Spring Boot Application (Docker Container)"
+        subgraph "Request Entry Point"
+            Filter[<fa:fa-filter> CorrelationIdFilter<br><i>Adds Trace ID</i>] --> Controller
+            Controller[<fa:fa-server> StegoController<br><i>REST API Endpoints</i>]
+            ExceptionHandler[<fa:fa-shield-alt> GlobalExceptionHandler<br><i>Formats Error Responses</i>]
+            Controller -- Catches Exceptions --> ExceptionHandler
+        end
+
+        subgraph "Core Business Logic"
+            Service[<fa:fa-concierge-bell> SteganographyService<br><i>Orchestrates Workflows</i>]
+        end
+
+        subgraph "Utility Services"
+            CapacitySvc[<fa:fa-calculator> CapacityUtilService<br><i>Estimates required space</i>]
+            AesSvc[<fa:fa-lock> AesUtilService<br><i>PBKDF2 Key Derivation, AES Encryption</i>]
+            LsbSvc[<fa:fa-magic> LsbUtilService<br><i>Hides data in image pixels</i>]
+            LargeFileSvc[<fa:fa-file-import> LargeFileEncryptionService<br><i>Handles large file streams</i>]
+        end
+
+        subgraph "Data & Storage Layer"
+            Repo[<fa:fa-book> StegoDataRepository<br><i>JPA interface to DB</i>]
+            StorageSvc[<fa:fa-folder-open> StorageService<br><i>Manages file system I/O</i>]
+        end
+
+        subgraph "Background Processing"
+            CleanupTask[<fa:fa-trash-alt> OrphanCleanupTask<br><i>Scheduled Job</i>]
+        end
+    end
+
+    subgraph "External Systems"
+        DB[(<fa:fa-database> MySQL Database<br><i>Stores encoding metadata</i>)]
+        FS[/<fa:fa-hdd> File System<br><i>Docker Volume for stego-images</i>/]
+    end
+
+    %% --- FLOWS ---
+    User -- "1. POST /encode (Image, Data, Password)" --> Filter
+    Controller -->|2. Calls| Service
+
+    Service -->|3. Early check| CapacitySvc
+    Service -->|4. Encrypts data| AesSvc
+    Service -- "4a. (For large files)" --> LargeFileSvc
+    Service -->|5. Embeds encrypted data| LsbSvc
+    Service -->|6. Saves stego-image| StorageSvc
+    Service -->|7. Saves metadata| Repo
+
+    Repo -->|JPA| DB
+    StorageSvc -->|Writes/Reads| FS
+    CleanupTask -->|Deletes old files| StorageSvc
+    CleanupTask -->|Checks DB references| Repo
+
+    style User fill:#D5E8D4,stroke:#82B366
+    style GH_Repo fill:#f5f5f5,stroke:#333
+    style DockerHub fill:#DAE8FC,stroke:#6C8EBF
+    style DB fill:#DAE8FC,stroke:#6C8EBF
+    style FS fill:#DAE8FC,stroke:#6C8EBF
+```
+
+## Demo
+
+[![Watch the demo video](https://img.youtube.com/vi/TEHwmlSL3ag/0.jpg)](https://youtu.be/TEHwmlSL3ag)
+
 ## Docker Hub
 
 The official Docker image for this project is available on Docker Hub. You can pull it directly to run the application without building it from the source.