docs: add visual pattern map with Mermaid diagrams

PATTERNS.md

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+# Design Patterns — Complete Visual Reference
+
+A comprehensive visual map of all **152** design patterns implemented in this repository, organized by category.
+
+> For pattern source code, browse each module directory. For the website, visit [java-design-patterns.com](https://java-design-patterns.com/patterns/).
+
+---
+
+## Pattern Landscape
+
+```mermaid
+mindmap
+  root((Design Patterns 152 total))
+    Creational
+      18 patterns
+      Object creation
+    Structural
+      26 patterns
+      Object composition
+    Behavioral
+      43 patterns
+      Object interaction
+    Concurrency
+      22 patterns
+      Multi-threading
+    Architectural
+      25 patterns
+      System structure
+    Functional
+      6 patterns
+      Functional style
+    Idiom
+      10 patterns
+      Language idioms
+    Integration
+      2 patterns
+      System integration
+```
+
+---
+
+## Creational Patterns
+*18 patterns — focused on object creation mechanisms, aiming to create objects suited to the situation.*
+
+```mermaid
+flowchart LR
+    C([🏗️ Creational\n18 patterns])
+
+    C --> AF[Abstract Factory]
+    C --> B[Builder]
+    C --> CO[Context Object]
+    C --> CV[Converter]
+    C --> DI[Dependency Injection]
+    C --> F[Factory]
+    C --> FK[Factory Kit]
+    C --> FM[Factory Method]
+    C --> MN[Monostate]
+    C --> MT[Multiton]
+    C --> OM[Object Mother]
+    C --> OP[Object Pool]
+    C --> P[Property]
+    C --> PT[Prototype]
+    C --> R[Registry]
+    C --> S[Singleton]
+    C --> SB[Step Builder]
+    C --> VO[Value Object]
+
+    style C fill:#4CAF50,color:#fff,stroke:#388E3C
+```
+
+---
+
+## Structural Patterns
+*26 patterns — focused on how classes and objects are composed to form larger structures.*
+
+```mermaid
+flowchart LR
+    S([🔩 Structural\n26 patterns])
+
+    S --> AD[Abstract Document]
+    S --> AP[Adapter]
+    S --> AM[Ambassador]
+    S --> BR[Bridge]
+    S --> BD[Business Delegate]
+    S --> CO[Composite]
+    S --> CE[Composite Entity]
+    S --> CV[Composite View]
+    S --> DE[Decorator]
+    S --> DL[Delegation]
+    S --> EV[Embedded Value]
+    S --> EA[Event Aggregator]
+    S --> FA[Facade]
+    S --> FL[Flux]
+    S --> FW[Flyweight]
+    S --> FC[Front Controller]
+    S --> MK[Marker]
+    S --> MD[Module]
+    S --> PC[Page Controller]
+    S --> PO[Page Object]
+    S --> PR[Proxy]
+    S --> RO[Role Object]
+    S --> SI[Separated Interface]
+    S --> ST[Strangler]
+    S --> TM[Table Module]
+    S --> TW[Twin]
+
+    style S fill:#2196F3,color:#fff,stroke:#1565C0
+```
+
+---
+
+## Behavioral Patterns
+*43 patterns — focused on communication and responsibility between objects.*
+
+```mermaid
+flowchart LR
+    B([🔄 Behavioral\n43 patterns])
+
+    B --> AV[Acyclic Visitor]
+    B --> BC[Bytecode]
+    B --> CA[Caching]
+    B --> CR[Chain of Responsibility]
+    B --> CB[Circuit Breaker]
+    B --> CM[Command]
+    B --> DL[Data Locality]
+    B --> DF[Dirty Flag]
+    B --> DB[Double Buffer]
+    B --> EO[Extension Objects]
+    B --> FT[Feature Toggle]
+    B --> GL[Game Loop]
+    B --> IM[Identity Map]
+    B --> IF[Intercepting Filter]
+    B --> IN[Interpreter]
+    B --> IT[Iterator]
+    B --> LE[Leader Election]
+    B --> ME[Mediator]
+    B --> MM[Memento]
+    B --> NO[Null Object]
+    B --> OB[Observer]
+    B --> PA[Parameter Object]
+    B --> PR[Partial Response]
+    B --> PI[Pipeline]
+    B --> PP[Poison Pill]
+    B --> PM[Presentation Model]
+    B --> PQ[Priority Queue]
+    B --> RT[Retry]
+    B --> SV[Servant]
+    B --> SH[Sharding]
+    B --> SP[Spatial Partition]
+    B --> SC[Special Case]
+    B --> SF[Specification]
+    B --> ST[State]
+    B --> SG[Strategy]
+    B --> SS[Subclass Sandbox]
+    B --> TM[Template Method]
+    B --> TH[Throttling]
+    B --> TR[Trampoline]
+    B --> TS[Transaction Script]
+    B --> TO[Type Object]
+    B --> UM[Update Method]
+    B --> VI[Visitor]
+
+    style B fill:#FF9800,color:#fff,stroke:#E65100
+```
+
+---
+
+## Concurrency Patterns
+*22 patterns — focused on multi-threaded and parallel programming.*
+
+```mermaid
+flowchart LR
+    C([⚡ Concurrency\n22 patterns])
+
+    C --> AO[Active Object]
+    C --> AM[Async Method Invocation]
+    C --> BK[Balking]
+    C --> CO[Commander]
+    C --> EA[Event Asynchronous]
+    C --> EQ[Event Queue]
+    C --> GS[Guarded Suspension]
+    C --> HA[Half-Sync Half-Async]
+    C --> LF[Leader Followers]
+    C --> LO[Lockable Object]
+    C --> MW[Master Worker]
+    C --> MO[Monitor]
+    C --> OL[Optimistic Offline Lock]
+    C --> PC[Producer Consumer]
+    C --> PR[Promise]
+    C --> QL[Queue-Based Load Leveling]
+    C --> RE[Reactor]
+    C --> RW[Reader-Writer Lock]
+    C --> SA[Saga]
+    C --> TL[Thread-Local Storage]
+    C --> TP[Thread Pool]
+    C --> VN[Version Number]
+
+    style C fill:#9C27B0,color:#fff,stroke:#6A1B9A
+```
+
+---
+
+## Architectural Patterns
+*25 patterns — focused on the overall structure and organization of a system.*
+
+```mermaid
+flowchart LR
+    A([🏛️ Architectural\n25 patterns])
+
+    A --> AG[Aggregator Microservices]
+    A --> AP[API Gateway]
+    A --> CS[Client Session]
+    A --> CQ[CQRS]
+    A --> DA[DAO]
+    A --> DB[Data Bus]
+    A --> DM[Data Mapper]
+    A --> DTO[Data Transfer Object]
+    A --> DO[Domain Model]
+    A --> ED[Event-Driven Architecture]
+    A --> ES[Event Sourcing]
+    A --> HX[Hexagonal]
+    A --> LA[Layers]
+    A --> MM[Metadata Mapping]
+    A --> MVC[Model-View-Controller]
+    A --> MVI[Model-View-Intent]
+    A --> MVP[Model-View-Presenter]
+    A --> MVVM[Model-View-ViewModel]
+    A --> NO[Naked Objects]
+    A --> RP[Repository]
+    A --> SE[Serialized Entity]
+    A --> SL[Service Layer]
+    A --> SC[Service Locator]
+    A --> SW[Service-to-Worker]
+    A --> UW[Unit of Work]
+
+    style A fill:#F44336,color:#fff,stroke:#B71C1C
+```
+
+---
+
+## Functional Patterns
+*6 patterns — focused on functional programming principles in an OO context.*
+
+```mermaid
+flowchart LR
+    F([λ Functional\n6 patterns])
+
+    F --> CP[Collection Pipeline]
+    F --> CB[Combinator]
+    F --> CU[Currying]
+    F --> FI[Filterer]
+    F --> FL[Fluent Interface]
+    F --> MO[Monad]
+
+    style F fill:#009688,color:#fff,stroke:#00695C
+```
+
+---
+
+## Idiom Patterns
+*10 patterns — language-specific patterns and coding conventions for Java.*
+
+```mermaid
+flowchart LR
+    I([☕ Idiom\n10 patterns])
+
+    I --> AA[Arrange Act Assert]
+    I --> CB[Callback]
+    I --> CL[Collecting Parameter]
+    I --> DC[Double-Checked Locking]
+    I --> DD[Double Dispatch]
+    I --> EA[Execute Around]
+    I --> LL[Lazy Loading]
+    I --> MI[Mute Idiom]
+    I --> PD[Private Class Data]
+    I --> RA[Resource Acquisition Is Initialization]
+
+    style I fill:#795548,color:#fff,stroke:#3E2723
+```
+
+---
+
+## Integration Patterns
+*2 patterns — focused on integrating systems and services.*
+
+```mermaid
+flowchart LR
+    N([🔗 Integration\n2 patterns])
+
+    N --> FF[Fanout Fan-in]
+    N --> TR[Tolerant Reader]
+
+    style N fill:#607D8B,color:#fff,stroke:#263238
+```
+
+---
+
+## Pattern Count by Category
+
+```mermaid
+xychart-beta
+    title "Design Patterns by Category"
+    x-axis ["Creational", "Structural", "Behavioral", "Concurrency", "Architectural", "Functional", "Idiom", "Integration"]
+    y-axis "Number of Patterns" 0 --> 50
+    bar [18, 26, 43, 22, 25, 6, 10, 2]
+```
+
+---
+
+## GoF Patterns at a Glance
+
+The original 23 Gang of Four patterns, mapped across the three classic GoF categories:
+
+```mermaid
+flowchart TD
+    GoF([Gang of Four\n23 Classic Patterns])
+
+    GoF --> CR[Creational]
+    GoF --> ST[Structural]
+    GoF --> BH[Behavioral]
+
+    CR --> AF[Abstract Factory]
+    CR --> BU[Builder]
+    CR --> FM[Factory Method]
+    CR --> PT[Prototype]
+    CR --> SG[Singleton]
+
+    ST --> AD[Adapter]
+    ST --> BR[Bridge]
+    ST --> CO[Composite]
+    ST --> DE[Decorator]
+    ST --> FA[Facade]
+    ST --> FW[Flyweight]
+    ST --> PR[Proxy]
+
+    BH --> CR2[Chain of Responsibility]
+    BH --> CM[Command]
+    BH --> IT[Iterator]
+    BH --> ME[Mediator]
+    BH --> MM[Memento]
+    BH --> OB[Observer]
+    BH --> SA[State]
+    BH --> SV[Strategy]
+    BH --> TM[Template Method]
+    BH --> VI[Visitor]
+    BH --> IN[Interpreter]
+
+    style GoF fill:#212121,color:#fff,stroke:#000
+    style CR fill:#4CAF50,color:#fff,stroke:#388E3C
+    style ST fill:#2196F3,color:#fff,stroke:#1565C0
+    style BH fill:#FF9800,color:#fff,stroke:#E65100
+```