fix: make beacons session-only, slower and QSY-aware (#171)

Forgotten beacons kept filling the chat while nobody was at the station.

- The two enable switches are session state now: they start off, are
  never read from preferences.xml and are always stored as "false", so
  neither a stored switch nor an older release reading a newer file can
  start a beacon. The in-code default was "on" and started a beacon
  whenever the file was unreadable or had no <beaconCQ> block.
- The minimum interval rises from 1 to 5 minutes; the bundled template
  ships 10 instead of 1. Smaller stored values are raised when the
  timer is scheduled.
- BeaconFrequencyGuard switches a beacon off once a logger-reported
  transceiver frequency lies more than 2 kHz from the one reported when
  the beacon was switched on. UCXLog RadioInfo and Win-Test STATUS feed
  it wherever they already set MYQRG/SECONDQRG. Without SO2R the single
  radio stands for both categories, with SO2R each radio for its own.

Manual (DE/EN), changelog, website and PROJECT_CONTEXT updated.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NJ1tUJVmWChD9V5Pg7uH8X

website/src/features/macros.md

@@ -174,7 +174,7 @@ Each chat category has its own enable setting and message template. Both categor
 
 Global variables are evaluated again on every timer run. A QRG changed by the logger can therefore be included in the next beacon without editing its template.
 
-The completely resolved beacon text must not exceed 120 characters. The configured minimum interval is one minute.
+The completely resolved beacon text must not exceed 120 characters. The configured minimum interval is five minutes.
 
 A suitable template is: