Tests: run in a sandbox that can't touch real app data, telemetry or the shared database

On a maintainer's Mac the compatibility-database key is in the Keychain, so a
test that reached install reporting published fake reports. Every test module
now imports tests/sandbox.py first, which points app data at a throwaway
directory (new FRAME_CONTROL_DATA_DIR), turns telemetry off and sends the
database nowhere.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tests/test_server.py

@@ -5,6 +5,7 @@ request guards and input validation, which all run before any SSH call.
 
 Run: python3 -m unittest discover -s tests
 """
+import sandbox  # noqa: F401  (first: keeps tests off real data and services)
 import http.client
 import io
 import json