feat(scripts): added --ref flag for installing specific git refs

- Added --ref flag to install specific tags, branches, or commits from source or binary releases.
- Enabled source installation from git refs by cloning and checking out the specified reference.
- Added git availability check for source installations with --ref flag.
- Updated README with usage examples for --ref flag on both shell and PowerShell installers.

scripts/install.ps1

@@ -4,10 +4,14 @@
 # Or with options:
 #   & ([scriptblock]::Create((irm https://raw.githubusercontent.com/can1357/oh-my-pi/main/scripts/install.ps1))) -Source
 #   & ([scriptblock]::Create((irm https://raw.githubusercontent.com/can1357/oh-my-pi/main/scripts/install.ps1))) -Binary
+#   & ([scriptblock]::Create((irm https://raw.githubusercontent.com/can1357/oh-my-pi/main/scripts/install.ps1))) -Source -Ref v3.20.1
+#   & ([scriptblock]::Create((irm https://raw.githubusercontent.com/can1357/oh-my-pi/main/scripts/install.ps1))) -Source -Ref main
+#   & ([scriptblock]::Create((irm https://raw.githubusercontent.com/can1357/oh-my-pi/main/scripts/install.ps1))) -Binary -Ref v3.20.1
 
 param(
     [switch]$Source,
-    [switch]$Binary
+    [switch]$Binary,
+    [string]$Ref
 )
 
 $ErrorActionPreference = "Stop"
@@ -26,6 +30,15 @@ function Test-BunInstalled {
     }
 }
 
+function Test-GitInstalled {
+    try {
+        $null = Get-Command git -ErrorAction Stop
+        return $true
+    } catch {
+        return $false
+    }
+}
+
 function Install-Bun {
     Write-Host "Installing bun..."
     irm bun.sh/install.ps1 | iex
@@ -35,18 +48,70 @@ function Install-Bun {
 
 function Install-ViaBun {
     Write-Host "Installing via bun..."
-    bun install -g $Package
+    if ($Ref) {
+        if (-not (Test-GitInstalled)) {
+            throw "git is required for -Ref when installing from source"
+        }
+
+        $tmpRoot = Join-Path ([System.IO.Path]::GetTempPath()) ("omp-install-" + [System.Guid]::NewGuid().ToString("N"))
+        New-Item -ItemType Directory -Force -Path $tmpRoot | Out-Null
+
+        try {
+            $repoUrl = "https://github.com/$Repo.git"
+            $cloneOk = $false
+            try {
+                git clone --depth 1 --branch $Ref $repoUrl $tmpRoot | Out-Null
+                $cloneOk = $true
+            } catch {
+                $cloneOk = $false
+            }
+
+            if (-not $cloneOk) {
+                git clone $repoUrl $tmpRoot | Out-Null
+                Push-Location $tmpRoot
+                try {
+                    git checkout $Ref | Out-Null
+                } finally {
+                    Pop-Location
+                }
+            }
+
+            $packagePath = Join-Path $tmpRoot "packages\coding-agent"
+            if (-not (Test-Path $packagePath)) {
+                throw "Expected package at $packagePath"
+            }
+
+            bun install -g $packagePath
+        } finally {
+            Remove-Item -Recurse -Force $tmpRoot -ErrorAction SilentlyContinue
+        }
+    } else {
+        bun install -g $Package
+    }
+
     Write-Host ""
     Write-Host "✓ Installed omp via bun" -ForegroundColor Green
     Write-Host "Run 'omp' to get started!"
 }
 
 function Install-Binary {
-    # Get latest release
-    Write-Host "Fetching latest release..."
-    $Release = Invoke-RestMethod -Uri "https://api.github.com/repos/$Repo/releases/latest"
+    if ($Ref) {
+        Write-Host "Fetching release $Ref..."
+        try {
+            $Release = Invoke-RestMethod -Uri "https://api.github.com/repos/$Repo/releases/tags/$Ref"
+        } catch {
+            throw "Release tag not found: $Ref`nFor branch/commit installs, use -Source with -Ref."
+        }
+    } else {
+        Write-Host "Fetching latest release..."
+        $Release = Invoke-RestMethod -Uri "https://api.github.com/repos/$Repo/releases/latest"
+    }
+
     $Latest = $Release.tag_name
-    Write-Host "Latest version: $Latest"
+    if (-not $Latest) {
+        throw "Failed to fetch release tag"
+    }
+    Write-Host "Using version: $Latest"
 
     # Download binary
     $Url = "https://github.com/$Repo/releases/download/$Latest/$BinaryName"
@@ -71,6 +136,10 @@ function Install-Binary {
 }
 
 # Main logic
+if ($Ref -and -not $Source -and -not $Binary) {
+    $Source = $true
+}
+
 if ($Source) {
     if (-not (Test-BunInstalled)) {
         Install-Bun