feat(coding-agent): isolate SproutClaw namespace from upstream pi

Use piConfig name sproutclaw and configDir .sproutclaw so commands, env vars,
and project config no longer collide with the stock pi install.

Co-authored-by: Cursor <cursoragent@cursor.com>

test.ps1

@@ -1,6 +1,9 @@
 $ErrorActionPreference = "Stop"
 
 $scriptDir = Split-Path -Parent $MyInvocation.MyCommand.Path
+if (-not $env:SPROUTCLAW_CODING_AGENT_DIR) {
+	$env:SPROUTCLAW_CODING_AGENT_DIR = Join-Path $scriptDir ".sproutclaw\agent"
+}
 $noEnv = $false
 $forwardArgs = New-Object System.Collections.Generic.List[string]