removed hard coded shader start up

docs/FORKING_RENDER_CADENCE_BASE.md

@@ -65,7 +65,7 @@ Do not move DeckLink, NDI, file I/O, shader compilation, or control handling int
 
 Before cutting a long-lived fork, fix or decide these items:
 
-- Remove hardcoded `happy-accident` assumptions in `src/app/AppConfig.h` and `src/runtime/shader/RuntimeSlangShaderCompiler.cpp`.
+- Keep `runtimeShaderId` empty in checked-in config unless this repo intentionally wants a default startup shader again.
 - Align remaining runtime third-party discovery with CMake. Font atlas generation now checks `MSDF_ATLAS_GEN_ROOT`, `THIRD_PARTY_ROOT`, `3rdParty`, and `video-io-3rdParty`; shader compiler lookup still needs the same treatment for Slang.
 - Make `config/runtime-host.json` portable. Current checked-in defaults include a local NDI source name and DeckLink output.
 - Decide whether the fork keeps the Slang shader package contract. If not, retire or clearly isolate `shaders/SHADER_CONTRACT.md`, shader package UI, and shader manifest tests.

docs/openapi.yaml

@@ -640,6 +640,8 @@ components:
           type: number
         runtimeShaderId:
           type: string
+          description: Optional startup shader id used only when no saved runtime layer stack is restored.
+          default: ""
       additionalProperties: false
     HostVideoInputConfig:
       type: object