Fix reliability, security, and correctness issues across codebase

[jwinarske]

Reliability fixes:

• signal_handler.h: Replace non-async-signal-safe spdlog call in signal handler with ::write() to prevent deadlocks/crashes
• login1_manager_client.cc: Fix iterator invalidation UB in destructor (erase-while-iterating via views::keys); replace with .clear()
• hostname1_client.cc: Fix inverted condition in printHostname1() that printed StaticHostname only when empty (2 locations)
• udisks2_partition_table.h: Fix wrong proxy base class (Partition_proxy instead of PartitionTable_proxy)
• udisks2_manager.cc: Add missing cleanup in onInterfacesRemoved() for all 9 interface types (was log-only, leaked objects)
• timedate1_client.cc: Replace thread-unsafe std::localtime() with localtime_r()
• upower_client.h: Simplify redundant operator-precedence expression
• udisks2_monitor_daemon.cc: Replace infinite while(true)/sleep loop with monitorLoop() and signal handling for graceful shutdown
• connman/main.cc: Fix exit code from 1 to 0 on normal termination
• avahi/main.cc: Fix typo "NSSS upport" -> "NSS Support"
• horipad input_reader.h: Remove duplicate #include

Security fixes:

• xbox_controller.cc, dual_sense.cc, horipad_steam.cc: Add null guard before input_reader_->stop() in udev remove callback
• hidraw.hpp: Fix ::toupper UB with signed char by using unsigned char lambda; add .contains("UNIQ") guard before .at() access
• xbox_controller.cc, dual_sense.cc: Fix ::tolower UB same way
• All 3 input_reader.cc: Add HID_MAX_DESCRIPTOR_SIZE bounds check on desc_size from ioctl before using it
• hidraw.hpp, udev_monitor.hpp: Replace direct spdlog includes with centralized logging.h; convert spdlog:: calls to LOG_* macros

Other:

• logging.h: British "recognised" -> US English "recognized"
• CMakeLists.txt: Add flatpak subdirectory
• All modified files formatted with clang-format-19