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/Package.swift

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+// swift-tools-version: 6.4
+
+import PackageDescription
+
+let package = Package(
+    name: "HelloPlaydate",
+    products: [
+        // The Playdate Simulator loads the game as pdex.dylib.
+        .library(name: "pdex", type: .dynamic, targets: ["HelloPlaydate"]),
+    ],
+    dependencies: [
+        .package(path: "../.."),
+    ],
+    targets: [
+        .target(
+            name: "HelloPlaydate",
+            dependencies: [.product(name: "PlayDate", package: "play-date")]
+        ),
+    ]
+)

Examples/HelloPlaydate/README.md

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+# 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.

Examples/HelloPlaydate/Source/pdxinfo

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+name=Hello Playdate
+author=Röck+Cöde
+description=Minimal example for the play-date Swift bindings
+bundleID=com.rock-n-code.hello-playdate
+version=0.1
+buildNumber=1

Examples/HelloPlaydate/Sources/HelloPlaydate/Game.swift

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+//
+//  Game.swift
+//  A minimal Playdate game built on the play-date Swift bindings: a
+//  bouncing box, a crank-aimed needle, button logging, and a system menu
+//  item.
+//
+
+import CPlaydate
+import PlayDate
+
+@_cdecl("eventHandler")
+public func eventHandler(
+    pointer: UnsafeMutableRawPointer,
+    event: PDSystemEvent,
+    argument: UInt32
+) -> Int32 {
+    if case .initialize = SystemEvent(event: event, argument: argument) {
+        Playdate.initialize(with: pointer)   // must happen before anything else
+        Game.shared.start()
+    }
+
+    return 0
+}
+
+final class Game {
+    nonisolated(unsafe) static let shared = Game()
+
+    private var x: Float = 200
+    private var y: Float = 120
+    private var dx: Float = 3
+    private var dy: Float = 2
+    private let boxSize = 24
+
+    func start() {
+        Display.setRefreshRate(50)
+
+        System.addMenuItem(title: "reset") { _ in
+            Game.shared.reset()
+        }
+
+        System.setUpdateCallback {
+            Game.shared.update()
+            return true   // redraw the display this frame
+        }
+    }
+
+    private func reset() {
+        x = 200
+        y = 120
+    }
+
+    private func update() {
+        moveBox()
+        handleInput()
+        draw()
+    }
+
+    private func moveBox() {
+        let width = Float(Display.width)
+        let height = Float(Display.height)
+
+        x += dx
+        y += dy
+        if x < 0 || x > width - Float(boxSize) { dx = -dx }
+        if y < 24 || y > height - Float(boxSize) { dy = -dy }
+    }
+
+    private func handleInput() {
+        let (_, pushed, _) = System.buttonState
+        if pushed.contains(.a) {
+            System.log("A pressed at \(System.currentTimeMilliseconds)ms")
+        }
+        if pushed.contains(.b) {
+            (dx, dy) = (-dx, -dy)
+        }
+    }
+
+    private func draw() {
+        Graphics.clear(color: .white)
+        Graphics.drawText("Hëllo from Swift — Ⓑ reverses", x: 8, y: 4)
+        Graphics.fillRect(x: Int(x), y: Int(y), width: boxSize, height: boxSize, color: .black)
+
+        if !System.isCrankDocked {
+            // A needle from the screen center pointing where the crank points.
+            let radians = System.crankAngle * .pi / 180
+            let centerX = Display.width / 2
+            let centerY = Display.height / 2
+            Graphics.drawLine(
+                x1: centerX, y1: centerY,
+                x2: centerX + Int(40 * sinf(radians)),
+                y2: centerY - Int(40 * cosf(radians)),
+                width: 2, color: .xor)
+        }
+
+        System.drawFPS(x: 380, y: 4)
+    }
+}

Examples/HelloPlaydate/build.sh

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+#!/bin/sh
+#
+# Builds HelloPlaydate.pdx for the Playdate Simulator: compiles the game as
+# a dylib, places it in the pdc source folder, and runs the SDK's pdc.
+#
+# Device builds need the Embedded Swift + ARM toolchain setup described in
+# the repository README; this script covers the simulator only.
+
+set -eu
+cd "$(dirname "$0")"
+
+sdk_path="${PLAYDATE_SDK_PATH:-$HOME/Developer/PlaydateSDK}"
+
+swift build -c release
+bin_path="$(swift build -c release --show-bin-path)"
+cp "$bin_path/libpdex.dylib" Source/pdex.dylib
+
+"$sdk_path/bin/pdc" Source HelloPlaydate.pdx
+
+echo "Built HelloPlaydate.pdx — run it with:"
+echo "  open -a \"$sdk_path/bin/Playdate Simulator.app\" HelloPlaydate.pdx"