docs(release): prep v1.6.6 — Central install snippet, release status block, community links (PR-1.6.6) (#100)

Wires up the final pre-cut PR from the readiness taskboard. Brings README + CHANGELOG up to the shape v1.6.6 will ship in. cut-release.ps1 will flip the JitPack snippet to v1.6.6 at release time as usual; the Central snippet is already pinned at v1.6.6 since v1.6.5 was never on Central.

Changes:

  README install section restructured. Maven Central (io.github.demchaav:graphcompose:1.6.6) listed first as the primary path; the JitPack snippet stays as fallback / pre-v1.6.6 alternative.

  README hero adds a Maven Central badge alongside the JitPack badge.

  README gains a 'Release status' block under the badges: latest stable v1.6.5 / in develop v1.6.6 / planned next v1.6.7 + v1.7.0, with a link to the API stability policy.

  README footer 'Contributing & releases' section gains links to CODE_OF_CONDUCT.md, SECURITY.md, docs/api-stability.md, docs/templates/which-template-system.md - the community files were committed long ago but never linked from the README.

  CHANGELOG v1.6.6 — Planned summary expanded to three paragraphs: what shipped, zero-breaking guarantee, migration-from-v1.6.5 sentence ('no code changes required; optionally swap to the Central coordinates').

Verification: ./mvnw test -pl . - 1033 tests, 0 failures (~91s). Doc guards green - JitPack snippet pinned to current pom version (1.6.5); Central snippet uses lowercase artifactId so the VersionConsistencyGuardTest regex doesn't scan it (intentional - Central versions are bumped manually in release-prep PRs).

After this PR merges, the v1.6.6 cut runs through graphcompose-release-engineer: cut-release.ps1 flips JitPack snippet to v1.6.6, dates the CHANGELOG, tags v1.6.6, pushes; release.yml creates the GitHub Release; publish.yml uploads to Maven Central (assuming the four secrets are wired); javadoc.io auto-mirrors within minutes.

Author: DemchaAV

CHANGELOG.md

@@ -5,10 +5,25 @@ follow semantic versioning; release dates are ISO 8601.
 
 ## v1.6.6 — Planned
 
-First Maven Central release. Adds publishable sources/javadoc jars,
-GPG-signed artifacts, a binary-compatibility gate against v1.6.5, and
-the metadata Maven Central requires. Zero breaking changes; users on
-JitPack continue to resolve through the existing coordinates.
+**First Maven Central release.** GraphCompose now ships under
+`io.github.demchaav:graphcompose:1.6.6` alongside the existing
+JitPack distribution. The release adds publishable sources/javadoc
+jars, GPG-signed artefacts, a binary-compatibility gate against
+v1.6.5, the metadata Maven Central requires, and a substantial
+documentation polish for the maturity / stability / migration story.
+
+**Zero breaking changes from v1.6.5.** Existing JitPack callers continue
+to resolve through the same coordinates; existing API surface compiles
+and runs unchanged (validated by the new `japicmp` gate against the
+v1.6.5 baseline). New: the `@Beta` annotation marker, the `@since 1.0.0`
+class-level Javadoc on entry-point packages, and a curated docs pass
+(decision guide for the two template surfaces, examples maturity index,
+explicit API stability policy).
+
+**Migration from v1.6.5:** no code changes required. Optionally swap
+the JitPack `<dependency>` for the Maven Central equivalent
+(`io.github.demchaav:graphcompose:1.6.6`); both publish paths continue
+to ship the same artefact.
 
 ### Build
 

README.md

@@ -12,12 +12,19 @@
 <p align="center">
   <a href="https://github.com/DemchaAV/GraphCompose/actions/workflows/ci.yml?query=branch%3Amain"><img src="https://img.shields.io/github/actions/workflow/status/DemchaAV/GraphCompose/ci.yml?branch=main&style=for-the-badge&label=CI" alt="CI"/></a>
   <a href="https://github.com/DemchaAV/GraphCompose/releases/latest"><img src="https://img.shields.io/github/v/release/DemchaAV/GraphCompose?style=for-the-badge&label=Release" alt="Latest release"/></a>
+  <a href="https://central.sonatype.com/artifact/io.github.demchaav/graphcompose"><img src="https://img.shields.io/maven-central/v/io.github.demchaav/graphcompose?style=for-the-badge&label=Maven%20Central" alt="Maven Central"/></a>
   <a href="https://jitpack.io/#DemchaAV/GraphCompose"><img src="https://img.shields.io/jitpack/v/github/DemchaAV/GraphCompose?style=for-the-badge&label=JitPack" alt="JitPack"/></a>
   <img src="https://img.shields.io/badge/Java-17%2B-orange?style=for-the-badge&logo=openjdk" alt="Java 17+"/>
   <img src="https://img.shields.io/badge/PDFBox-3.0-red?style=for-the-badge" alt="PDFBox 3.0"/>
   <img src="https://img.shields.io/badge/License-MIT-blue?style=for-the-badge" alt="MIT License"/>
 </p>
 
+> **Release status** &mdash;
+> 🟢 **Latest stable**: [v1.6.5](https://github.com/DemchaAV/GraphCompose/releases/tag/v1.6.5) (JitPack)
+> &nbsp;·&nbsp; 🟡 **In develop**: v1.6.6 (Maven Central debut; zero breaking from v1.6.5)
+> &nbsp;·&nbsp; ⚪ **Planned next**: v1.6.7 (dependency cleanup), v1.7.0 (new canonical DSL primitives)
+> &nbsp;·&nbsp; See [API stability policy](./docs/api-stability.md) for tier definitions.
+
 <p align="center">
   <a href="https://demchaav.github.io/GraphCompose/"><b>Live Showcase</b></a>
   &nbsp;·&nbsp;
@@ -87,6 +94,22 @@ GraphCompose uses PDFBox under the hood as the rendering backend &mdash; the com
 
 ## Installation
 
+### Maven Central (primary, from v1.6.6)
+
+```xml
+<dependency>
+    <groupId>io.github.demchaav</groupId>
+    <artifactId>graphcompose</artifactId>
+    <version>1.6.6</version>
+</dependency>
+```
+
+```kotlin
+dependencies { implementation("io.github.demchaav:graphcompose:1.6.6") }
+```
+
+### JitPack (fallback / pre-v1.6.6)
+
 ```xml
 <repositories>
     <repository><id>jitpack.io</id><url>https://jitpack.io</url></repository>
@@ -206,7 +229,8 @@ document.pageFlow().addCanvas(523, 360, canvas -> canvas
 - [Examples gallery](./examples/README.md) &mdash; every runnable example with PDF preview
 
 ### Contributing & releases
-- [Migration v1.5 → v1.6](./docs/roadmaps/migration-v1-5-to-v1-6.md) · [Release process](./docs/contributing/release-process.md) · [Contributing](./CONTRIBUTING.md)
+- [Contributing](./CONTRIBUTING.md) · [Code of conduct](./CODE_OF_CONDUCT.md) · [Security policy](./SECURITY.md) · [Release process](./docs/contributing/release-process.md)
+- [API stability policy](./docs/api-stability.md) · [Which template system?](./docs/templates/which-template-system.md) · [Migration v1.5 → v1.6](./docs/roadmaps/migration-v1-5-to-v1-6.md)
 
 ## Companion projects