Fix Debian package build issues

- Remove debian/compat file (conflicts with Build-Depends)
- Fix debian/install to use correct readme.md filename
- Update verify-deb.sh to mark debian/compat as optional
- Add -Zgzip flag to dpkg-buildpackage for compatibility
  (uses gzip instead of zstd for better compatibility)
- Update verify-deb.sh to check optional vs required files

Package now builds and installs successfully on systems
without zstd support.

debian/install

@@ -1,7 +1,7 @@
 src/sensorpajen/*.py opt/sensorpajen/src/sensorpajen/
 scripts/approve-sensors.sh opt/sensorpajen/scripts/
 pyproject.toml opt/sensorpajen/
-README.md usr/share/doc/sensorpajen/
+readme.md usr/share/doc/sensorpajen/
 INSTALL.md usr/share/doc/sensorpajen/
 ROADMAP.md usr/share/doc/sensorpajen/
 config/*.example usr/share/doc/sensorpajen/examples/