Release v26.5.2 (#2797)

Six days of community momentum after 1.0: 123 commits since v26.5.1.

Highlights:
- AetherModem AX.25 packet decoder Phase-0 (jensenpat)
- FreeDV/RADE ergonomics — sync indicator, far-end metadata, EOO
callsign (NF0T)
- 4m/2m bands on FLEX-6500 and FLEX-6700 via ModelCapabilities
- PersistentDialog architecture sweep — 10+ dialogs migrated
- Spectrum/panadapter stabilization — restore window, dBm echo
smoothing,
  Ctrl-drag dBm/waterfall, macOS GPU lifecycle (rfoust)
- Protocol hardening — M-message severity, hex meter num,
FlexWaveformModel,
  tx_slice_mode

Bumps version 26.5.1 → 26.5.2 in CMakeLists.txt, README.md, CLAUDE.md;
regenerates WhatsNewData.cpp from CHANGELOG.md (100 releases, 758
items).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ten9876