Fix PeakCAN listen-only mode with native PCAN-Basic configuration

[RMBmd]

Problem

SavvyCAN currently represents listen-only mode as bit 0 of QCanBusDevice::UserKey. Qt's peakcan backend does not consume that key; it supports bitrate/CAN-FD configuration but rejects the custom UserKey. Consequently, checking Listen Only in SavvyCAN can still initialize a PEAK interface in active mode, where it may acknowledge frames or emit active error flags.

This is observable during sensitive diagnostic transitions such as UDS programming-session entry: PCAN-View in native listen-only mode is non-intrusive, while SavvyCAN with the same UI option can alter bus behavior.

Fix

This change:

• Detects the Qt peakcan backend.
• Maps Qt PeakCAN interface names (usb0-usb15, pci0-pci15) to PCAN-Basic channel handles.
• Dynamically resolves PCAN-Basic rather than introducing a link-time dependency.
• Calls CAN_SetValue(..., PCAN_LISTEN_ONLY, ...) before QCanBusDevice::connectDevice() initializes the channel.
• Reads the parameter back after initialization and disconnects if requested listen-only mode cannot be verified.
• Refuses to open a PeakCAN channel when listen-only was requested but native configuration fails, so the application fails closed rather than silently joining the bus actively.
• Prevents SavvyCAN frame transmission while a bus is configured as listen-only.
• Preserves the existing UserKey behavior for non-Peak Qt SerialBus backends.
• Avoids reporting a failed/rejected connection as connected during the reconnect loop.

PCAN-Basic is already the runtime API used by Qt's PeakCAN plugin, so this does not add a new external runtime requirement for users of that backend.

Validation

The exact production commit was compiled successfully with:

• Linux x64, Qt 5/qmake
• Windows x64, MSVC 2022, Qt 5/qmake

The validation branch used a temporary same-repository workflow; this submitted branch contains only the production source change.

Hardware acceptance criteria for a PEAK interface are:

1. SavvyCAN connects with Listen Only selected.
2. PCAN-Basic reports PCAN_LISTEN_ONLY=ON after initialization.
3. The PEAK interface produces no ACK bits, active error flags, or application transmissions.
4. A diagnostic/programming sequence behaves identically to the PCAN-View listen-only baseline.

Reference

PEAK documents PCAN_LISTEN_ONLY as the controller's passive monitoring mode and permits it to be configured before channel initialization:

https://www.peak-system.com/produktcd/Develop/PC%20interfaces/Windows/PCAN-Basic%20API/PCAN-Parameter_Documentation.pdf

[RMBmd]

Upstream submission

The production branch is based directly on collin80/SavvyCAN:master and contains one commit affecting one file. Open the upstream comparison and select Create pull request:

https://github.com/collin80/SavvyCAN/compare/master...RMBmd:fix/peakcan-native-listen-only?expand=1

The connected GitHub App can write to this fork but is not installed with write permission on collin80/SavvyCAN, so GitHub rejected automated creation of the cross-fork PR with HTTP 403.

Validated build

The exact commit 011062fd19dd9cb6bfd3f39311b007f72a290cfb compiled successfully in temporary CI on:

• Linux x64 with Qt 5/qmake
• Windows x64 with Visual Studio 2022 and Qt 5/qmake

The temporary validation PR was closed after both jobs passed. The production branch contains no temporary workflow files.

[RMBmd]

Superseded by upstream SavvyCAN PR collin80#1104:

collin80#1104

The exact submitted commit compiled successfully and has passed physical
PCAN-USB Pro listen-only validation.