refactor(build): consolidate envs to production/debug/test; add compiler hardening flags

- Replace 11 per-frequency build environments with 3 role-based targets
  (production, debug, test) using shared [env] base section
- Move LoRa frequency and sender-ID config from build flags into config.h
  so all variants build from the same source
- Add -fstack-protector-strong, -D_FORTIFY_SOURCE=2, -Wformat-security
- Add Unity test framework to lib_deps for pio test support
- Add __pycache__/ to .gitignore

.gitignore

@@ -3,3 +3,5 @@
 .vscode/c_cpp_properties.json
 .vscode/launch.json
 .vscode/ipch
+
+__pycache__/