fix(install): npm-cli.js path + CONTRIBUTING/PR template

install.sh: bundled Node 的 INSTALL_NPM 之前指向 bin/npm shell wrapper,
通过 \"node npm\" 调用会失败。改为 lib/node_modules/npm/bin/npm-cli.js,
并加 run_npm() 帮助函数区分系统 Node(用 npm 可执行)和 bundled Node。

install.ps1: 系统 Node 场景下 npm-cli.js 路径推导脆弱。改为按候选路径
依次试探,找不到则直接退到 npm.cmd。

新增 CONTRIBUTING.md + .github/PULL_REQUEST_TEMPLATE.md,规范 PR 流程,
减少空白/无说明 PR(对应 issue PR #36)。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

install/install.ps1

@@ -93,12 +93,18 @@ if ($sysNode) {
     if ($major -ge 20) {
         Write-Green "  [OK] System Node.js $sysVer found, reusing"
         $INSTALL_NODE = "node"
-        $npmCmd = (Get-Command npm -ErrorAction SilentlyContinue).Source
-        $npmRoot = Split-Path (Split-Path $npmCmd)
-        $NPM_CLI = "$npmRoot\node_modules\npm\bin\npm-cli.js"
-        if (-not (Test-Path $NPM_CLI)) {
-            $npmPrefix = & node -e "console.log(process.execPath.replace(/[\\\/]node\.exe$/i,''))" 2>$null
-            $NPM_CLI = "$npmPrefix\node_modules\npm\bin\npm-cli.js"
+        # Resolve npm-cli.js next to node.exe; fall back to npm.cmd as a launcher.
+        $nodeExeDir = Split-Path $sysNode.Source -Parent
+        $candidates = @(
+            "$nodeExeDir\node_modules\npm\bin\npm-cli.js",
+            "$env:APPDATA\npm\node_modules\npm\bin\npm-cli.js",
+            "$env:ProgramFiles\nodejs\node_modules\npm\bin\npm-cli.js"
+        )
+        $NPM_CLI = $null
+        foreach ($p in $candidates) { if (Test-Path $p) { $NPM_CLI = $p; break } }
+        if (-not $NPM_CLI) {
+            # Last resort: use npm.cmd directly (don't pass through node.exe)
+            $NPM_CLI = (Get-Command npm -ErrorAction SilentlyContinue).Source
         }
         $USE_SYSTEM_NODE = $true
     }