Add DocC documentation and a runnable example game

- DocC catalog (Sources/PlayDate/PlayDate.docc) with a curated landing
  page and a Getting Started article; swift-docc-plugin wired up for
  `swift package generate-documentation`, and a GitHub Pages deployment
  workflow renders docs on every push to main.
- Examples/HelloPlaydate: a minimal game (bouncing box, crank needle,
  button handling, system menu item) whose build.sh compiles the game as
  a dylib and produces a runnable simulator .pdx via the SDK's pdc.
  Verified: the pdx builds and exports the eventHandler entry point.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Examples/HelloPlaydate/README.md

@@ -0,0 +1,23 @@
+# Hello Playdate
+
+A minimal game built on the `play-date` bindings: a bouncing box, a
+crank-aimed needle, button handling, a system menu item, and an FPS counter.
+
+## Build and run (Playdate Simulator)
+
+With the Playdate SDK installed (and the one-time
+`Scripts/install-pkgconfig.sh` setup from the repository root done):
+
+```sh
+./build.sh
+open -a "$HOME/Developer/PlaydateSDK/bin/Playdate Simulator.app" HelloPlaydate.pdx
+```
+
+The script compiles the game as a dylib, places it in `Source/` next to
+`pdxinfo`, and runs the SDK's `pdc` to produce `HelloPlaydate.pdx`.
+
+## Device builds
+
+Running on hardware requires the Embedded Swift + ARM toolchain pipeline
+(see the repository README and Apple's swift-playdate-examples for the
+Makefile setup). This example covers the simulator workflow only.