chore: standardize markdown formatting and workflow

.github/workflows/markdown.yml

@@ -0,0 +1,22 @@
+name: Markdown
+
+# Runs unconditionally on every PR to main -- deliberately NO `paths:` filter.
+# This job is a required status check, and a path-filtered required check never
+# reports on PRs that touch no markdown, blocking them forever at
+# "Expected - waiting for status to be reported".
+
+on:
+  pull_request:
+    branches: [main]
+  workflow_dispatch:
+
+jobs:
+  # Job ID is the check-run context name the branch ruleset matches on.
+  markdown:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
+        with:
+          node-version: "24"
+      - run: npx --yes prettier@3.9.6 --check "**/*.md"

.prettierrc.json

@@ -0,0 +1,12 @@
+{
+  "overrides": [
+    {
+      "files": ["**/*.md"],
+      "options": {
+        "proseWrap": "always",
+        "printWidth": 80,
+        "embeddedLanguageFormatting": "off"
+      }
+    }
+  ]
+}

README.md

@@ -2,34 +2,35 @@
 
 A slide (15) puzzle implemented in Dart and Flutter.
 
-**Live Demo**: [https://kevmoo.github.io/slide_puzzle/](https://kevmoo.github.io/slide_puzzle/)
+**Live Demo**:
+[https://kevmoo.github.io/slide_puzzle/](https://kevmoo.github.io/slide_puzzle/)
 
 <p align="center">
   <img src="docs/screen_shot.png" alt="Slide Puzzle Screenshot" width="350">
 </p>
 
 ## Features
 
-* **Multiple Themes**:
-  * **Simple**: Minimalist numerical tiles with smooth physics animations.
-  * **Seattle**: Image-based slider dividing photography across the grid.
-  * **Plaster**: Stylized typographic display using custom font geometry.
-* **Physics & Animations**: Spring simulation, velocity decay, and directional
+- **Multiple Themes**:
+  - **Simple**: Minimalist numerical tiles with smooth physics animations.
+  - **Seattle**: Image-based slider dividing photography across the grid.
+  - **Plaster**: Stylized typographic display using custom font geometry.
+- **Physics & Animations**: Spring simulation, velocity decay, and directional
   drag physics.
-* **Built-in Solver**:
-  * Shortest-path A* solver utilizing Manhattan distances and linear conflicts.
-  * Step-by-step hint button and automated playback solve mode.
-* **Auto-Play & Metrics**: Automatic random move ticker with move and tile
+- **Built-in Solver**:
+  - Shortest-path A* solver utilizing Manhattan distances and linear conflicts.
+  - Step-by-step hint button and automated playback solve mode.
+- **Auto-Play & Metrics**: Automatic random move ticker with move and tile
   counters.
 
 ## Architecture
 
-* **High-Performance Nibble Packing**: Boards $\le 4 \times 4$ use `_PuzzleSmart`
-  backed by a `Uint32List` packed into 4-bit nibbles for zero-allocation state
-  transitions.
-* **Incremental Delta Tracking**: Tile movements calculate distance deltas and
+- **High-Performance Nibble Packing**: Boards $\le 4 \times 4$ use
+  `_PuzzleSmart` backed by a `Uint32List` packed into 4-bit nibbles for
+  zero-allocation state transitions.
+- **Incremental Delta Tracking**: Tile movements calculate distance deltas and
   linear conflict adjustments incrementally without full board rescans.
-* **Generic Fallback**: Arbitrary board dimensions ($>16$ tiles, e.g. 5×5)
+- **Generic Fallback**: Arbitrary board dimensions ($>16$ tiles, e.g. 5×5)
   gracefully fall back to `_PuzzleSimple` (`Uint8List`).
 
 ## Development

ios/Runner/Assets.xcassets/LaunchImage.imageset/README.md

@@ -1,5 +1,8 @@
 # Launch Screen Assets
 
-You can customize the launch screen with your own desired assets by replacing the image files in this directory.
+You can customize the launch screen with your own desired assets by replacing
+the image files in this directory.
 
-You can also do it by opening your Flutter project's Xcode project with `open ios/Runner.xcworkspace`, selecting `Runner/Assets.xcassets` in the Project Navigator and dropping in the desired images.
+You can also do it by opening your Flutter project's Xcode project with
+`open ios/Runner.xcworkspace`, selecting `Runner/Assets.xcassets` in the Project
+Navigator and dropping in the desired images.