docs(examples): add a single-slide "Available on Maven Central" banner rendered to PPTX (#432)

* docs(examples): add a single-slide Maven Central banner rendered to PPTX

MavenBannerPptxExample composes an "Available on Maven Central" brand
banner — wordmark, Maven coordinate card, capability tags and a
code -> layout -> PDF/PPTX diagram — as one full-bleed CanvasLayerNode on
a 960x540 slide, then emits it through the fixed-layout PPTX backend via
DocumentSession.buildPptx(). The canvas containers use OVERFLOW_VISIBLE so
the panels render as native, editable PowerPoint shapes and text rather
than rasterised pictures. A vector PDF copy and a PNG preview reuse the
same composition.

* docs(examples): branch the banner flow into both output backends

The layout box now feeds a vertical distribution bus that forks into the
PDF icon (top) and the PPTX icon (bottom), each landing with an arrowhead,
so the code -> layout -> output flow visibly terminates at both backends
instead of stopping at a short shared stub.

* test(examples): guard the Maven banner's native-PPTX output and register it

Adds MavenBannerNativeShapeTest, which builds the banner through the fixed
PPTX backend and asserts the slide stays native shapes and text except the
single rasterised SVG checkmark — pinning the "editable in PowerPoint"
promise the way TwinOutputNativeShapeTest pins the twin-output slide.
Registers MavenBannerPptxExample in GenerateAllExamples so the showcase
smoke test exercises it end-to-end. Also sources the 960x540 canvas from
DocumentPageSize.SLIDE_16_9, adds @SInCE 2.1.0, gives each arrowhead a
unique node name, and corrects the class Javadoc to read PDF/PPTX.

* docs(examples): list the Maven banner in the gallery with PDF/PPTX previews

Adds the flagship gallery row in examples/README.md and commits the rendered
maven-banner.pdf and maven-banner.pptx under assets/readme/examples/ so the
row's PDF/PPTX links resolve, matching the Twin Output treatment.

* docs(changelog): note the Maven Central banner example under v2.1.0

Adds a v2.1.0 Documentation entry for MavenBannerPptxExample — the
single-slide "Available on Maven Central" banner rendered to PPTX, its
GenerateAllExamples registration, gallery previews and native-shape guard.

Author: DemchaAV

CHANGELOG.md

@@ -184,6 +184,16 @@ follow semantic versioning; release dates are ISO 8601.
   deck open in PowerPoint with the headline text frame selected — the
   committed artifacts land 69 native shapes with only the clip-masked logo
   as a picture.
+- New `MavenBannerPptxExample` flagship: a single 16:9 "Available on Maven
+  Central" brand slide — the `GraphCompose` wordmark, an
+  `io.github.demchaav:graph-compose` coordinate card, `JAVA 17+ / PDF / PPTX /
+  AUTO-PAGINATION` tags and a `code → layout → PDF/PPTX` diagram whose amber
+  connectors branch to both backends — composed as one full-bleed
+  `CanvasLayerNode` and emitted as an editable PowerPoint slide via
+  `buildPptx()`. Registered in `GenerateAllExamples` and listed in the
+  examples gallery with committed PDF/PPTX previews; a native-shape guard
+  (`MavenBannerNativeShapeTest`) pins the slide to a single picture (the badge
+  checkmark) with the panels, tags, code and diagram all native.
 - `docs/architecture/backend-capability-matrix.md` — a per-capability matrix
   of what each render backend supports and which class implements it,
   maintained as part of every capability-changing PR.

assets/readme/examples/maven-banner.pdf

@@ -63,6 +63,7 @@ are with the canonical DSL, then jump to its detailed section below.
 | **Engine Showcase** | Single-page cinematic brand promo — semantic-graph → polished-PDFs visual metaphor with rounded clip frame, magazine headline lockup, KPI cards, capability columns; source of the README hero image | [Source](src/main/java/com/demcha/examples/flagships/EngineShowcase.java) |
 | **Engine Deck** | Multi-page **landscape** capability deck — page 1 is a banner infographic (DSL code → engine → backends → **real rendered-document thumbnails**), then an authoring-pipeline walkthrough, and two pages of **real benchmark data** (GraphCompose vs iText 9 vs JasperReports) loaded from a bundled result file and drawn as tables + native charts; the landscape companion to Engine Showcase. The same composition also renders as a **geometry-identical PowerPoint deck** (one page = one editable slide) through `buildPptx()` | [PDF](../assets/readme/examples/engine-deck.pdf) · [Source](src/main/java/com/demcha/examples/flagships/EngineDeckExample.java) · [PPTX source](src/main/java/com/demcha/examples/flagships/EngineDeckPptxExample.java) |
 | **Twin Output** | The dual-output hook stated by the artifact itself — a single 16:9 page written once and emitted **twice from the same session**: `buildPdf()` and `buildPptx(...)` produce a print-ready PDF and a PowerPoint slide with identical geometry where text, panels, and vectors stay native, editable shapes (only the clip-masked logo art lands as a picture); the root README shows PowerPoint's own render of the slide next to the PDF | [PDF](../assets/readme/examples/twin-output.pdf) · [PPTX](../assets/readme/examples/twin-output.pptx) · [Source](src/main/java/com/demcha/examples/flagships/TwinOutputExample.java) |
+| **Maven Central Banner** | Single 16:9 "Available on Maven Central" brand slide — the `GraphCompose` wordmark, an `io.github.demchaav:graph-compose` coordinate card, `JAVA 17+ / PDF / PPTX / AUTO-PAGINATION` tags, and a `code → layout → PDF/PPTX` diagram whose amber connectors branch to both backends — composed as one full-bleed `CanvasLayerNode` and emitted as an editable PowerPoint slide via `buildPptx()`; panels and text stay native shapes, only the badge checkmark rasterises | [PDF](../assets/readme/examples/maven-banner.pdf) · [PPTX](../assets/readme/examples/maven-banner.pptx) · [Source](src/main/java/com/demcha/examples/flagships/MavenBannerPptxExample.java) |
 
 ### 🧱 Core DSL
 

assets/readme/examples/maven-banner.pptx

@@ -49,6 +49,7 @@
 import com.demcha.examples.flagships.FeatureCatalogExample;
 import com.demcha.examples.flagships.FinancialReportExample;
 import com.demcha.examples.flagships.MasterShowcaseExample;
+import com.demcha.examples.flagships.MavenBannerPptxExample;
 import com.demcha.examples.flagships.ModuleFirstFileExample;
 import com.demcha.examples.flagships.TwinOutputExample;
 import com.demcha.examples.templates.coverletter.CvBlueBannerLetterV2Example;
@@ -215,6 +216,7 @@ public static void main(String[] args) throws Exception {
         System.out.println("Generated: " + BusinessReportExample.generate());
         System.out.println("Generated: " + EngineDeckExample.generate());
         System.out.println("Generated: " + EngineDeckPptxExample.generate());
+        System.out.println("Generated: " + MavenBannerPptxExample.generate());
         System.out.println("Generated: " + TwinOutputExample.generate());
         System.out.println("Generated: " + FinancialReportExample.generate());
         System.out.println("Generated: " + BookTemplateExample.generate());