feat: one-command installers for macOS, Linux and Windows

deployment/install.sh (curl | bash) and install.ps1 (irm | iex) check for
Docker, install uv when it is missing or older than 0.8 (pinned 0.12.15 via
Astral's installer), install or upgrade the docsgpt package with
`uv tool install`, and hand the terminal to `docsgpt up` with any arguments.
On Linux without Docker the shell installer offers get.docker.com. Both run
entirely inside a function, so a download cut short runs nothing.

Releases attach both scripts next to the Compose file, which is where
docs.ac/install and docs.ac/install.ps1 will point. installer-lint.yml runs
shellcheck and the PowerShell parser; docker-image-verify.yml now installs
through install.sh. README, Quickstart, Docker-Deploying and the changelog
lead with the one-liner.

deployment/install.ps1

@@ -0,0 +1,94 @@
+# DocsGPT installer for Windows.
+#
+#   irm https://docs.ac/install.ps1 | iex
+#
+# Installs uv when it is missing or too old, installs the docsgpt Python
+# package with it, then runs `docsgpt up`, which sets up DocsGPT on Docker
+# Desktop and starts it. Running it again upgrades the package and keeps your
+# settings. To pass options to `docsgpt up`:
+#
+#   & ([scriptblock]::Create((irm https://docs.ac/install.ps1))) --domain docs.example.com --yes
+#
+# Environment:
+#   DOCSGPT_VERSION         package version to install (default: the latest release)
+#   DOCSGPT_PACKAGE         install this instead of docsgpt from PyPI (a wheel path or URL)
+#   DOCSGPT_NO_MODIFY_PATH  set to 1 to leave PATH alone
+#
+# Everything runs inside a function, so a download cut short runs nothing, and
+# nothing calls `exit`, which would close the window `iex` runs in.
+
+function Install-DocsGPT {
+    param([string[]]$UpArguments)
+
+    $ErrorActionPreference = 'Stop'
+    $UvVersion = '0.12.15'
+    $UvMinVersion = [version]'0.8.0'
+
+    function Say([string]$Message) { Write-Host "==> $Message" }
+
+    if (-not (Get-Command docker -ErrorAction SilentlyContinue)) {
+        throw 'DocsGPT runs on Docker. Install Docker Desktop (https://docs.docker.com/desktop/setup/install/windows-install/), start it, and run this again.'
+    }
+
+    # uv installs and upgrades the package, and brings Python 3.12 when the system has none.
+    $uv = $null
+    $candidates = @(
+        (Get-Command uv -ErrorAction SilentlyContinue | Select-Object -ExpandProperty Source -First 1),
+        (Join-Path $HOME '.local\bin\uv.exe'),
+        (Join-Path $HOME '.cargo\bin\uv.exe')
+    ) | Where-Object { $_ -and (Test-Path $_) }
+    foreach ($candidate in $candidates) {
+        $found = "$(& $candidate --version 2>$null)" -replace '^uv\s+([0-9.]+).*$', '$1'
+        if ($found -match '^\d+\.\d+(\.\d+)?$' -and [version]$found -ge $UvMinVersion) {
+            $uv = $candidate
+            break
+        }
+    }
+    if (-not $uv) {
+        $uvDir = Join-Path $HOME '.local\bin'
+        Say "Installing uv $UvVersion into $uvDir"
+        $env:UV_INSTALL_DIR = $uvDir
+        $env:UV_NO_MODIFY_PATH = '1'
+        $env:UV_PRINT_QUIET = '1'
+        # A child PowerShell, so nothing the uv installer does can end this session.
+        $shell = (Get-Process -Id $PID).Path
+        & $shell -NoProfile -ExecutionPolicy Bypass -Command "irm https://astral.sh/uv/$UvVersion/install.ps1 | iex"
+        $uv = Join-Path $uvDir 'uv.exe'
+        if (-not (Test-Path $uv)) { throw "uv did not install into $uvDir" }
+    }
+
+    if ($env:DOCSGPT_VERSION -and $env:DOCSGPT_PACKAGE) {
+        throw 'Set DOCSGPT_VERSION or DOCSGPT_PACKAGE, not both.'
+    }
+    if ($env:DOCSGPT_PACKAGE) {
+        Say "Installing docsgpt from $env:DOCSGPT_PACKAGE"
+        & $uv tool install --reinstall --python 3.12 $env:DOCSGPT_PACKAGE
+    } elseif ($env:DOCSGPT_VERSION) {
+        Say "Installing docsgpt $env:DOCSGPT_VERSION"
+        & $uv tool install --force --python 3.12 "docsgpt==$env:DOCSGPT_VERSION"
+    } else {
+        Say 'Installing the latest docsgpt'
+        & $uv tool install --upgrade --python 3.12 docsgpt
+    }
+    if ($LASTEXITCODE -ne 0) { throw 'Installing the docsgpt package failed.' }
+
+    $binDir = "$(& $uv tool dir --bin)".Trim()
+    $docsgpt = Join-Path $binDir 'docsgpt.exe'
+    if (-not (Test-Path $docsgpt)) { throw "The docsgpt command is missing from $binDir." }
+    if (($env:Path -split ';') -notcontains $binDir) {
+        if ($env:DOCSGPT_NO_MODIFY_PATH -eq '1') {
+            Say "Add $binDir to PATH to run docsgpt from a new terminal"
+        } else {
+            & $uv tool update-shell *> $null
+            Say "Added $binDir to PATH for new terminals"
+        }
+        $env:Path = "$binDir;$env:Path"
+    }
+
+    & $docsgpt up @UpArguments
+    if ($LASTEXITCODE -ne 0) {
+        Write-Error "docsgpt up exited with code $LASTEXITCODE. Run it again after fixing the problem above: docsgpt up" -ErrorAction Continue
+    }
+}
+
+Install-DocsGPT -UpArguments $args