ci: keep the Command Line Tools on the macOS 26 SDK, which Xcode 26.6's linker can read [claude-test]

On runner image 20261013.0424.1 the Command Line Tools' MacOSX.sdk points to a macOS 27 SDK, and the backend build's links failed on it ("tapi error: malformed file … unknown architecture arm64e.x1-macos") although DEVELOPER_DIR selects Xcode 26.6. use-macos26-sdk.sh points it back at the MacOSX26.5.sdk installed beside it, in all three macOS jobs.

This push runs the name cases with Claude again (run 4 failed before the app was built), after the smoke test with its new checks.

.github/workflows/ios-sim.yml

@@ -76,6 +76,9 @@ jobs:
           xcrun --show-sdk-path
           ls /Library/Developer/CommandLineTools/SDKs || true
 
+      - name: Use the macOS 26 SDK
+        run: scripts/ci/ios-sim/use-macos26-sdk.sh
+
       # without ~/.cabal, cabal 3.10 keeps its store in XDG directories, not where setup-haskell reports it
       - name: Use ~/.cabal for cabal
         run: echo "CABAL_DIR=$HOME/.cabal" >> "$GITHUB_ENV"
@@ -144,6 +147,9 @@ jobs:
           xcrun --show-sdk-path
           ls /Library/Developer/CommandLineTools/SDKs || true
 
+      - name: Use the macOS 26 SDK
+        run: scripts/ci/ios-sim/use-macos26-sdk.sh
+
       - name: Use ~/.cabal for cabal
         run: echo "CABAL_DIR=$HOME/.cabal" >> "$GITHUB_ENV"
 
@@ -212,6 +218,9 @@ jobs:
           ls /Library/Developer/CommandLineTools/SDKs || true
           xcrun simctl list runtimes
 
+      - name: Use the macOS 26 SDK
+        run: scripts/ci/ios-sim/use-macos26-sdk.sh
+
       - name: Download core library
         uses: actions/download-artifact@v4
         with: