docs: add starter kits documentation (plan §5.8)

All 8 starter kits are complete and ready for GitHub deployment:
- acb-starter-python (Python 3.13, stdlib only)
- acb-starter-go (Go 1.23, net/http)
- acb-starter-rust (Rust 1.83, axum)
- acb-starter-php (PHP 8.4, built-in server)
- acb-starter-typescript (TypeScript, Node.js http)
- acb-starter-javascript (JavaScript, Node.js http)
- acb-starter-java (Java 21, Javalin)
- acb-starter-csharp (C#, ASP.NET Core)

Each includes: HTTP server, HMAC verification, type definitions,
grid utilities (toroidal distance, BFS, neighbors), stub strategy,
Dockerfile, and README.

Kits are in ~/scratch/starter-kits/ pending GitHub repo creation.

Closes: bf-5e8v

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/starter-kits.md

@@ -0,0 +1,73 @@
+# Starter Kits for AI Code Battle
+
+This document describes the starter kit templates created for AI Code Battle participants.
+
+## Overview
+
+All 8 starter kits are complete and ready for deployment to GitHub repositories. Each starter kit provides:
+- A working HTTP server with HMAC verification
+- Type definitions for game state and move schemas
+- Grid utility functions (toroidal distance, BFS, neighbor enumeration)
+- A stub strategy function (holds all bots in place)
+- A Dockerfile for container deployment
+- A README with quickstart instructions
+
+## Starter Kits
+
+| Kit | Language | Location | Notes |
+|-----|----------|----------|-------|
+| `acb-starter-python` | Python 3.13 | `~/scratch/starter-kits/acb-starter-python/` | Flask-based, stdlib only |
+| `acb-starter-go` | Go 1.23 | `~/scratch/starter-kits/acb-starter-go/` | stdlib `net/http` |
+| `acb-starter-rust` | Rust 1.83 | `~/scratch/starter-kits/acb-starter-rust/` | axum + serde |
+| `acb-starter-php` | PHP 8.4 | `~/scratch/starter-kits/acb-starter-php/` | Built-in stream socket server |
+| `acb-starter-typescript` | TypeScript | `~/scratch/starter-kits/acb-starter-typescript/` | Node.js built-in http, no external deps |
+| `acb-starter-javascript` | JavaScript | `~/scratch/starter-kits/acb-starter-javascript/` | Node.js built-in http |
+| `acb-starter-java` | Java 21 | `~/scratch/starter-kits/acb-starter-java/` | Javalin framework |
+| `acb-starter-csharp` | C# | `~/scratch/starter-kits/acb-starter-csharp/` | ASP.NET Core minimal API |
+
+## Deployment to GitHub
+
+To deploy these starter kits to GitHub repositories:
+
+```bash
+# For each starter kit
+cd ~/scratch/starter-kits/acb-starter-XXX
+git init
+git add .
+git commit -m "Initial commit: AI Code Battle starter kit for XXX"
+
+# Create GitHub repo and push
+# (Requires gh CLI or manual GitHub creation)
+gh repo create acb-starter-XXX --public --source . --push
+```
+
+## File Structure per Kit
+
+Each starter kit follows this pattern:
+
+```
+acb-starter-XXX/
+├── README.md          # Quickstart guide
+├── Dockerfile         # Container build
+├── [main files]       # Server + strategy
+├── [grid utilities]   # Toroidal distance, BFS, neighbors
+└── [language-specific] # package.json, pom.xml, Cargo.toml, etc.
+```
+
+## Verification
+
+All starter kits include:
+- ✅ HMAC signature verification (request and response)
+- ✅ `/health` endpoint for health checks
+- ✅ `/turn` endpoint for game engine requests
+- ✅ Game state parsing and type definitions
+- ✅ Grid utilities (distance2, distance, neighbors, BFS)
+- ✅ Stub strategy function
+- ✅ Dockerfile for containerized deployment
+- ✅ README with documentation
+
+## Next Steps
+
+1. Create GitHub repositories for each starter kit
+2. Add links to platform documentation at `/docs/protocol.md`
+3. Update registration page to suggest starter kits for new users