feat(dist): crates.io + binstall + Windows install.ps1 + license files

Distribution prep on the road to public availability (plan steps 2–3a).

- Cargo.toml: publish-ready (drop publish=false; homepage/keywords/
  categories/exclude) + [package.metadata.binstall] with per-target
  overrides (linux-gnu->musl, windows-msvc->gnu/gnullvm). dry-run clean.
- scripts/install.ps1: Windows `irm | iex` one-liner — written but
  untested here (no PowerShell; validate on Windows). README Windows block.
- README.md (new); LICENSE-MIT + LICENSE-APACHE (dual, (c) Lazy
  Evaluation Ltd); CONTRIBUTING.md (inbound=outbound dual-license note).
- ADR-0055 Amendment 1 (install.ps1), ADR-0056 (crates.io/binstall),
  README index + plan updates.

The actual `cargo publish` remains a gated maintainer step (token,
irreversible) at a new tagged release; real cargo-binstall validation
pending.

scripts/install.ps1

@@ -0,0 +1,94 @@
+<#
+.SYNOPSIS
+    Download and install a prebuilt rdbms-playground binary (Windows).
+
+.DESCRIPTION
+    The Windows counterpart of scripts/install.sh. Detects the CPU
+    architecture, downloads the matching release .exe from the Gitea
+    releases, verifies its SHA-256 checksum, installs it to
+    %LOCALAPPDATA%\Programs\rdbms-playground, and adds that directory to
+    your user PATH.
+
+    Quick start:
+        irm https://git.lazyeval.net/oli/rdbms-playground/raw/branch/main/scripts/install.ps1 | iex
+
+    We ship gnu / gnullvm Windows builds (x86_64 / aarch64); this maps the
+    host architecture to the right asset.
+
+.PARAMETER Version
+    Install a specific tag (e.g. v0.2.0) instead of the latest release.
+    Defaults to $env:RDBMS_VERSION, else the latest release.
+
+.PARAMETER InstallDir
+    Install directory. Defaults to $env:RDBMS_INSTALL_DIR, else
+    %LOCALAPPDATA%\Programs\rdbms-playground.
+
+.NOTES
+    Written but NOT tested on Windows from this environment (no PowerShell
+    here) — validate on a real Windows host. The verified sibling is
+    install.sh (Linux/macOS).
+#>
+[CmdletBinding()]
+param(
+    [string]$Version = $env:RDBMS_VERSION,
+    [string]$InstallDir = $(if ($env:RDBMS_INSTALL_DIR) { $env:RDBMS_INSTALL_DIR } else { "$env:LOCALAPPDATA\Programs\rdbms-playground" })
+)
+
+Set-StrictMode -Version Latest
+$ErrorActionPreference = 'Stop'
+
+$Repo = 'https://git.lazyeval.net/oli/rdbms-playground'
+$Api = 'https://git.lazyeval.net/api/v1/repos/oli/rdbms-playground'
+$Bin = 'rdbms-playground'
+
+# Map the host CPU to the target triple we publish for Windows.
+$osArch = [System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture
+switch ($osArch) {
+    'X64' { $target = 'x86_64-pc-windows-gnu' }
+    'Arm64' { $target = 'aarch64-pc-windows-gnullvm' }
+    default { throw "install: unsupported CPU architecture: $osArch" }
+}
+
+# Resolve the release tag (explicit -Version, else the latest release).
+if (-not $Version) {
+    $Version = (Invoke-RestMethod -Uri "$Api/releases/latest").tag_name
+    if (-not $Version) { throw 'install: could not determine the latest release tag' }
+}
+
+$asset = "$Bin-$Version-$target.exe"
+$url = "$Repo/releases/download/$Version/$asset"
+
+$tmp = Join-Path $env:TEMP ([System.Guid]::NewGuid().ToString())
+New-Item -ItemType Directory -Path $tmp -Force | Out-Null
+try {
+    $exe = Join-Path $tmp "$Bin.exe"
+    $shaFile = "$exe.sha256"
+
+    Write-Host "downloading $asset ..."
+    Invoke-WebRequest -Uri $url -OutFile $exe
+    Invoke-WebRequest -Uri "$url.sha256" -OutFile $shaFile
+
+    # The sidecar is "<hash>  <name>"; compare just the hash.
+    $expected = ((Get-Content -Raw $shaFile) -split '\s+')[0].ToLower()
+    $actual = (Get-FileHash -Algorithm SHA256 -Path $exe).Hash.ToLower()
+    if ($expected -ne $actual) {
+        throw "install: checksum mismatch (expected $expected, got $actual) — refusing to install"
+    }
+
+    New-Item -ItemType Directory -Path $InstallDir -Force | Out-Null
+    $dest = Join-Path $InstallDir "$Bin.exe"
+    Move-Item -Path $exe -Destination $dest -Force
+    Write-Host "installed $Bin $Version -> $dest"
+
+    # Add the install dir to the user PATH (persistent) if it's not there.
+    $userPath = [Environment]::GetEnvironmentVariable('Path', 'User')
+    if (-not $userPath) { $userPath = '' }
+    if (($userPath -split ';') -notcontains $InstallDir) {
+        $newPath = if ($userPath) { "$userPath;$InstallDir" } else { $InstallDir }
+        [Environment]::SetEnvironmentVariable('Path', $newPath, 'User')
+        Write-Host "added $InstallDir to your user PATH — restart your shell to pick it up"
+    }
+}
+finally {
+    Remove-Item -Path $tmp -Recurse -Force -ErrorAction SilentlyContinue
+}