Build fixes found during first local compilation (qmake6 + g++ -Werror):
1. Logging category: nymea-plugininfocompiler generates 'dcV2C' (uppercase C)
from the JSON vendor name "V2C". All three source files used 'dcV2c'
(lowercase c) — corrected to 'dcV2C' in integrationpluginv2c.cpp,
trydanmodbustcpmaster.cpp, v2ctcpdiscovery.cpp.
2. modbus.pri: hardcoded include(/usr/include/nymea-modbus/modbus-tool.pri)
fails when libnymea-modbus-dev is not system-installed. Changed to a
conditional: checks $$[QT_INSTALL_PREFIX] first, then NYMEA_MODBUS_PATH
override, with a graceful fallback (warning + manual C++17 CONFIG flag).
The v2c plugin has MODBUS_CONNECTIONS empty so the tool loop is a no-op
either way; the fallback is safe.
3. debian/: add powersync-plugin-v2c package entry (control, .install,
changelog entry 1.15.0+etm4).
Build verified: libnymea_integrationpluginv2c.so links against libnymea.so.1,
libnymea-modbus.so.1, Qt6Network/SerialBus/Core, 0 compiler warnings
(with -Werror -Wall -Wextra -std=c++17).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
