Add Ultralight SDK submodule and update scripts

Add Ultralight SDK as a git submodule (ThirdParty/Ultralight-SDK, Windows branch) and update build/deploy tooling and docs to use the vendored SDK by default. Updated .gitmodules and added the submodule pointer; build-prismaui.bat and deploy-all.bat now default UL_SDK to the submodule path and build-prismaui.bat checks the submodule is initialized. The PowerShell linker script (scripts/setup-ultralight-link.ps1) now falls back to ThirdParty/Ultralight-SDK when no SdkPath is provided. Documentation and developer log updated (docs/setup.md, plugin/setup.md, docs/dev-log.md) to document submodule initialization and usage; ULTRALIGHT_SDK_PATH can still override the default. Run 'git submodule update --init --recursive' on clones to initialize the SDK.

scripts/setup-ultralight-link.ps1

@@ -1,11 +1,15 @@
 param(
-    [string]$SdkPath = "F:\UltralightSDK"
+    [string]$SdkPath = ""
 )
 
 $ErrorActionPreference = "Stop"
 
 $scriptDir = Split-Path -Parent $MyInvocation.MyCommand.Path
 $repoRoot = Split-Path -Parent $scriptDir
+
+if ([string]::IsNullOrWhiteSpace($SdkPath)) {
+    $SdkPath = Join-Path $repoRoot "ThirdParty\Ultralight-SDK"
+}
 $frameworkBuild = Join-Path $repoRoot "ThirdParty\framework-F4-Conversion\build"
 $linkPath = Join-Path $frameworkBuild "ultralight-1.4.0"