docs: actualizar tagline y diagrama de arquitectura en README

Reflejar que los wrappers conectan vía FFI o subprocess, y reemplazar
el diagrama ASCII por Mermaid para mejor legibilidad en GitHub.

Author: Kevinsillo

README.md

@@ -9,7 +9,7 @@
   <a href="https://github.com/Kevinsillo/anvildb/actions/workflows/tests.yml"><img src="https://github.com/Kevinsillo/anvildb/actions/workflows/tests.yml/badge.svg" alt="Tests"></a>
 </p>
 
-<p align="center"><strong>Embedded JSON document database powered by a Rust core, with language wrappers via FFI.</strong></p>
+<p align="center"><strong>Embedded JSON document database powered by a Rust core, with language wrappers via FFI or subprocess.</strong></p>
 
 <p align="center">Zero external dependencies. No MySQL, PostgreSQL, SQLite, or PDO required. Just your filesystem and raw speed.</p>
 
@@ -50,26 +50,17 @@ Want to create a wrapper for another language? See the [Wrapper Development Guid
 
 ## Architecture
 
+```mermaid
+graph TD
+    App[Application] --> Wrapper[Language Wrapper]
+
+    Wrapper -->|FFI · direct| Core[Rust Core Engine]
+    Wrapper -->|Subprocess · stdin/stdout| Server[anvildb-server] --> Core
+
+    Core --> FS[("Filesystem (.anvil)")]
 ```
-Application
-    |
-    v
-Language Wrapper (PHP, Python, etc.)
-    |                          |
-    | FFI (direct, fastest)    | Process (no extensions needed)
-    | JSON strings + handle    | JSON lines over stdin/stdout
-    v                          v
-Rust Core Engine           anvildb-server
-    |  - Write Buffer (dirty tracking + batched flush)
-    |  - LRU Cache (auto-invalidated)
-    |  - In-memory Indexes (Hash / Unique / Range)
-    |  - Query Engine (filter, join, sort, paginate)
-    |  - Schema Validation
-    |  - Codec (deflate compression + optional AES-256-GCM)
-    |  - Atomic Storage (temp file + rename)
-    v
-Filesystem (.anvil compressed + metadata.json)
-```
+
+**Core internals:** Write Buffer · LRU Cache · In-memory Indexes (Hash, Unique, Range) · Query Engine (filter, join, sort, paginate) · Schema Validation · Codec (deflate + AES-256-GCM) · Atomic Storage
 
 ## Performance