CI: install Go + gomobile if missing (for BitBox Flutter iOS bindings)

scripts/build_bitbox_flutter.sh invokes build_bindings.sh which calls
gomobile to generate iOS bindings for the Go BitBox client. Without
Go + gomobile on the Mac runner, that step fails with 'gomobile:
command not found'.

Adds an idempotent step: install Go via brew if missing, then 'go
install golang.org/x/mobile/cmd/{gomobile,gobind}@latest' if missing.
Self-hosted runner persists $GOPATH/bin between runs, so steady-state
is zero-cost after the first install.

Same conditional-install pattern as Flutter + CocoaPods.

.github/workflows/build-ios-sim.yml

@@ -62,11 +62,9 @@ jobs:
             pod --version
             exit 0
           fi
-          # Prefer Homebrew on macOS — no sudo, installs into its own prefix.
           if command -v brew >/dev/null; then
             brew install cocoapods
           else
-            # Fallback: user-local gem install (no sudo).
             export GEM_HOME="$HOME/.gem"
             export PATH="$GEM_HOME/bin:$PATH"
             echo "GEM_HOME=$HOME/.gem" >> "$GITHUB_ENV"
@@ -75,6 +73,27 @@ jobs:
           fi
           pod --version
 
+      - name: Install Go + gomobile (if missing)
+        run: |
+          if ! command -v go >/dev/null; then
+            if command -v brew >/dev/null; then
+              brew install go
+            else
+              echo "Go missing and brew not available"; exit 1
+            fi
+          fi
+          go version
+          # Ensure $(go env GOPATH)/bin is on PATH for subsequent steps.
+          GOPATH=$(go env GOPATH)
+          echo "$GOPATH/bin" >> "$GITHUB_PATH"
+          export PATH="$PATH:$GOPATH/bin"
+          # gomobile + gobind are needed by scripts/build_bitbox_flutter.sh
+          if ! command -v gomobile >/dev/null; then
+            go install golang.org/x/mobile/cmd/gomobile@latest
+            go install golang.org/x/mobile/cmd/gobind@latest
+          fi
+          which gomobile && gomobile version || true
+
       - name: Show toolchain
         run: |
           set -x

.github/workflows/build-ios-testflight.yml

@@ -76,6 +76,25 @@ jobs:
           fi
           pod --version
 
+      - name: Install Go + gomobile (if missing)
+        run: |
+          if ! command -v go >/dev/null; then
+            if command -v brew >/dev/null; then
+              brew install go
+            else
+              echo "Go missing and brew not available"; exit 1
+            fi
+          fi
+          go version
+          GOPATH=$(go env GOPATH)
+          echo "$GOPATH/bin" >> "$GITHUB_PATH"
+          export PATH="$PATH:$GOPATH/bin"
+          if ! command -v gomobile >/dev/null; then
+            go install golang.org/x/mobile/cmd/gomobile@latest
+            go install golang.org/x/mobile/cmd/gobind@latest
+          fi
+          which gomobile && gomobile version || true
+
       - name: Show toolchain
         run: |
           set -x