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.

docs/dev-log.md

@@ -7,6 +7,40 @@ failed experiments, successful tests, and next steps.
 
 ---
 
+## 2026-06-11 - Ultralight SDK Submodule
+
+### Summary
+Added the Ultralight SDK as a vendored git submodule on the `Windows` branch so the SDK travels with the repo across machines. Updated PrismaUI build/deploy scripts to default to the submodule path instead of a fixed local drive path.
+
+### Files Changed
+- `.gitmodules`
+- `ThirdParty/Ultralight-SDK` (new submodule)
+- `build-prismaui.bat`
+- `deploy-all.bat`
+- `scripts/setup-ultralight-link.ps1`
+- `plugin/setup.md`
+- `docs/setup.md`
+
+### Details
+- Submodule URL: `https://git.zambazosmedia.group/andrew/Ultralight-SDK.git`
+- Submodule branch: `Windows`
+- Default SDK path is now `ThirdParty/Ultralight-SDK`; `ULTRALIGHT_SDK_PATH` still overrides it
+- `build-prismaui.bat` checks that the Ultralight submodule is initialized before linking
+
+### Testing
+- `git submodule add -b Windows ...` completed successfully
+- Verified submodule checkout is on `Windows` at commit `c0395a49bd`
+- Build scripts not run in this session
+
+### Known Issues
+- None currently known
+
+### Next Steps
+- Run `build-prismaui.bat` on a clean clone to confirm junction linking and PrismaUI_F4 build
+- Commit submodule pointer and script/doc updates
+
+---
+
 ## 2026-06-05 - Locomotion Tier + Jump Takeoff Fix (Round 2)
 
 ### Summary

docs/setup.md

@@ -43,6 +43,23 @@ Windows version:
 Compiler version:
 ```
 
+## Git Submodules
+
+After cloning, initialize vendored dependencies:
+
+```bat
+git submodule update --init --recursive
+```
+
+This includes:
+
+* `ThirdParty/framework-F4-Conversion` — PrismaUI_F4 HTML overlay framework
+* `ThirdParty/Ultralight-SDK` — Ultralight SDK (`Windows` branch) for PrismaUI_F4 builds
+* `ThirdParty/GameNetworkingSockets-src` — networking library
+* `ThirdParty/xbyak` — assembler dependency
+
+`build-prismaui.bat` links the Ultralight SDK submodule into the PrismaUI build tree automatically. Override the SDK location with `ULTRALIGHT_SDK_PATH` if needed.
+
 ## Folder Notes
 
 Do not copy Fallout 4 game files into this repository.