feat(build-tool): add application icon and refresh MUO.ico (#2487)

## What

- **BuildTool now has a distinct application icon** — the MUO mark with a three-gear "settings" cluster in the bottom-right, colored by size (azure / steel / teal), wired in via `<ApplicationIcon>` in `BuildTool.csproj`. This differentiates the (now signed) build tool from the server in the taskbar/Explorer.
- **Refreshed `Projects/Application/MUO.ico`** — re-rendered from vector with the full Windows size ladder (16/32/48/64/128/256). The previous icon only carried 128/256 frames, so Windows had nothing proper for small sizes.
- **Added `branding/`** — the source SVGs (`muo.svg`, `gears.svg`, `build-tool.svg`) the `.ico` files are rasterized from.

## How

Both icons are rasterized from the branding SVGs (high-density render → Lanczos downscale per frame → packed into a 6-frame `.ico`). The rasterization script and its node deps are kept local under the gitignored `tools/` dir and intentionally not committed — `branding/` is the source of truth.

## Verification

- `dotnet build Projects/BuildTool/BuildTool.csproj` succeeds (0 warnings/errors).
- The embedded icon resource extracts from the produced `build-tool.exe`.
- Both `.ico`s validate as 6-frame Windows icons.

### Icons

<img width="150" height="150" alt="build-tool" src="https://github.com/user-attachments/assets/9c443947-4c26-46a3-ad9b-5f50630d90ad" />

Projects/BuildTool/BuildTool.csproj

@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
     <PropertyGroup>
         <OutputType>Exe</OutputType>
+        <ApplicationIcon>build-tool.ico</ApplicationIcon>
         <TargetFramework>net10.0</TargetFramework>
         <LangVersion>Preview</LangVersion>
         <ImportDirectoryBuildProps>false</ImportDirectoryBuildProps>