docs: add CI badge and dependency graph to README

Author: Mearman

README.md

@@ -1,11 +1,29 @@
 # byte-codec
 
-[![GitHub](https://img.shields.io/badge/GitHub-181717?logo=github&logoColor=white)](https://github.com/ExaDev/byte-codec) [![npm](https://img.shields.io/badge/npm-CB3837?logo=npm&logoColor=white)](https://www.npmjs.com/package/byte-codec) [![Release](https://img.shields.io/github/v/release/ExaDev/byte-codec)](https://github.com/ExaDev/byte-codec/releases/latest)
+[![GitHub](https://img.shields.io/badge/GitHub-181717?logo=github&logoColor=white)](https://github.com/ExaDev/byte-codec) [![npm](https://img.shields.io/badge/npm-CB3837?logo=npm&logoColor=white)](https://www.npmjs.com/package/byte-codec) [![Release](https://img.shields.io/github/v/release/ExaDev/byte-codec)](https://github.com/ExaDev/byte-codec/releases/latest) [![CI](https://img.shields.io/github/actions/workflow/status/ExaDev/byte-codec/ci.yml?branch=main)](https://github.com/ExaDev/byte-codec/actions)
 
 > Generic byte-level primitives (ByteWriter, ByteReader, CRC-32, deflate/inflate) and PNG/JPEG image encoding/decoding with zero PDF knowledge — the shared utility package for the documents.js family.
 
 Extracted from [pdf-codec](https://github.com/ExaDev/pdf-codec), where these utilities lived as a directory-isolated subgraph under `src/bytes/` + `src/image/` with no PDF imports. Both pdf-codec and documents.js consume them from this neutral home rather than one fetching byte utilities from a backend.
 
+byte-codec has no internal dependencies in the documents.js family — its only external dependency is [`fflate`](https://github.com/101arrowz/fflate) for raw DEFLATE/zlib compression. Both [pdf-codec](https://github.com/ExaDev/pdf-codec) and [documents.js](https://github.com/ExaDev/documents.js) depend on it:
+
+```mermaid
+graph TD
+    bytecodec("byte-codec")
+    pdfcodec("pdf-codec")
+    documents("documents.js")
+
+    bytecodec --> pdfcodec
+    bytecodec --> documents
+
+    click bytecodec "https://github.com/ExaDev/byte-codec" "byte-codec"
+    click pdfcodec "https://github.com/ExaDev/pdf-codec" "pdf-codec"
+    click documents "https://github.com/ExaDev/documents.js" "documents.js"
+
+    style bytecodec fill:#f9a825,stroke:#333,stroke-width:3px
+```
+
 ## Getting started
 
 Requires Node.js `>=20` and pnpm `11.6.0`.