fix: Linux CI sandbox prereqs, platform-aware tests, broader prompt stripping

- Add bubblewrap and socat to Linux CI apt-get install
- Make sandbox test assertions platform-aware (macFileSystem vs linuxFileSystem)
- Make /etc/shells test accept both macOS and Linux first-line format
- Broaden wrapped prompt fragment regex to handle path chars (ts/testWorkspace$)
- Fix continuation pattern to match user@host:path wrapped lines
- Apply stripCommandEchoAndPrompt to getOutput() in BasicExecuteStrategy
  (basic shell integration lacks reliable 133;C markers so getOutput()
  can include command echo)
- Keep RichExecuteStrategy getOutput() unstripped (rich integration
  has reliable markers)

.github/workflows/pr-linux-test.yml

@@ -42,7 +42,9 @@ jobs:
             libxkbfile-dev \
             libkrb5-dev \
             libgbm1 \
-            rpm
+            rpm \
+            bubblewrap \
+            socat
           sudo cp build/azure-pipelines/linux/xvfb.init /etc/init.d/xvfb
           sudo chmod +x /etc/init.d/xvfb
           sudo update-rc.d xvfb defaults