docs: add shellcheck to system dependencies installation

- Add shellcheck to Ubuntu/Debian system dependencies script
- Add shellcheck to macOS system dependencies script via Homebrew
- Update CI workflow to verify shellcheck installation

This ensures shellcheck is available for developers following the setup
documentation and validates the installation in CI testing.

Author: dannywillems

.github/workflows/test-docs-scripts.yml

@@ -69,6 +69,7 @@ jobs:
           protoc --version
           sqlite3 --version
           wasm-pack --version
+          shellcheck --version
 
   macos:
     name: Test System Setup Scripts (${{ matrix.os }})
@@ -125,6 +126,7 @@ jobs:
           protoc --version
           sqlite3 --version
           wasm-pack --version
+          shellcheck --version
 
   docker-ubuntu:
     name: Test Docker Setup Script (${{ matrix.os }})

website/docs/developers/scripts/setup/install-system-deps-macos.sh

@@ -10,4 +10,5 @@ brew install \
     protobuf \
     sqlite \
     git \
-    curl
+    curl \
+    shellcheck

website/docs/developers/scripts/setup/install-system-deps.sh

@@ -6,4 +6,5 @@ sudo apt install -y \
     protobuf-compiler \
     sqlite3 \
     git \
-    curl
+    curl \
+    shellcheck