Add web UI configuration_url to device info

[lnagel]

Adds a "Visit device" link to the Home Assistant device page that links
to the Komfovent device's web interface. This feature is similar to
what the WLED integration provides.

Changes:

• Add build_device_info() helper function that centralizes device info
  creation and includes the configuration_url
• Update all entity types to use the new helper function
• Include controller model (C6, C6M, C8) in device info
• Add unit tests for the new functionality

Closes #141

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.43%. Comparing base (882bcdf) to head (f77c04d).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #153      +/-   ##
==========================================
+ Coverage   90.33%   90.43%   +0.10%     
==========================================
  Files          18       18              
  Lines        1314     1328      +14     
  Branches      127      127              
==========================================
+ Hits         1187     1201      +14     
  Misses         95       95              
  Partials       32       32              

Files with missing lines	Coverage Δ
custom_components/komfovent/binary_sensor.py	88.88% <100.00%> (+0.20%)	⬆️
custom_components/komfovent/button.py	92.00% <100.00%> (+0.33%)	⬆️
custom_components/komfovent/climate.py	93.93% <100.00%> (+0.06%)	⬆️
custom_components/komfovent/datetime.py	90.69% <100.00%> (+0.22%)	⬆️
custom_components/komfovent/helpers.py	90.00% <100.00%> (+5.38%)	⬆️
custom_components/komfovent/number.py	76.19% <100.00%> (+0.28%)	⬆️
custom_components/komfovent/select.py	84.78% <100.00%> (+0.33%)	⬆️
custom_components/komfovent/sensor.py	85.86% <100.00%> (ø)
custom_components/komfovent/switch.py	88.88% <100.00%> (+0.31%)	⬆️