Refactor and document: fix cert filenames, add Doxygen, improve demo

Refactoring (issues 1,3,4,5,7,8,9,10 from review):
- Replace hardcoded cert filenames with certFile/keyFile properties
- Add 30s timeout to certificate trust QEventLoop
- Cache servers() QVariantList instead of rebuilding per call
- Validate URLs before passing to QtOpcUa
- Use ComboBox valueRole for robust enum mapping
- Add certificate trust dialog to demo
- Remove unnecessary RowLayout wrapper
- Remove debug output from BuildDeps.cmake

Documentation:
- Add Doxygen file blocks to all C++ files
- Document AuthMode enum, toAuthenticationInformation(), key
  Q_INVOKABLE methods, certificateTrustRequested signal contract
- Convert section banners to standard format
- Add file/target comments to CMake and QML files

1 files changed, 4 insertions, 0 deletions

diff --git a/src/BobinkAuth.cpp b/src/BobinkAuth.cpp
index fed1da2..03ae2cf 100644
--- a/src/BobinkAuth.cpp
+++ b/src/BobinkAuth.cpp
@@ -1,3 +1,7 @@
+/**
+ * @file   BobinkAuth.cpp
+ * @brief  BobinkAuth implementation.
+ */
 #include "BobinkAuth.h"
 
 BobinkAuth::BobinkAuth(QObject *parent)