Add optional control-channel source affinity - #1157

Summary

Adds an opt-in per-system sourceAffinity setting for trunked systems. When enabled, Trunk Recorder keeps that system's control-channel decoder on its startup-assigned source: same-source control-channel retunes continue normally, while an alternate outside the assigned source is skipped with a warning.

The setting defaults to false, so existing cross-source scanning behavior remains unchanged. Voice-recorder source selection is not affected.

Why

Moving a control-channel decoder between sources requires disconnecting and rebuilding that decoder within the shared GNU Radio top block. In a multi-system field deployment, repeated cross-source rebuilds from one marginal system correlated with resets and brief decode interruptions on another stable system, and one rebuild stalled in the graph restart path. Operators who intentionally place every valid control channel for a site within one source need a way to prevent an unusable out-of-range candidate from causing those shared-graph rebuilds.

This is an opt-in safety boundary, not a replacement for cross-source scanning. It must only be enabled when the assigned source covers every control channel the system may use.

Changes

• Parse and document the optional sourceAffinity system setting.
• Preserve same-source retunes when affinity is enabled.
• Block out-of-range cross-source control-channel retunes with a specific warning.
• Leave the default retune path and voice-recorder source selection unchanged.
• Add a focused decision test for all enabled/disabled and covered/uncovered cases.

Validation

• Native Ubuntu 24.04 Release build completed successfully, including bundled plugins.
• ctest --output-on-failure: 1/1 passed.

Closes #1156