Implement a rigctld protocol emulator that allows WSJT-X, fldigi, and
other Hamlib-compatible software to control the radio. Includes:

- RigctlProtocol: pure protocol parser/responder (no I/O), supports
  get/set freq, mode, VFO, PTT, split, dump_state, batch commands
- RigctlServer: QTcpServer wrapper, multi-client, per-client state
- RigctlPty: openpty() virtual serial port with /tmp/AetherSDR-CAT symlink

Mode mapping verified against FLEX-8600 fw v1.4.0.0. Thread-safe writes
via QMetaObject::invokeMethod with Qt::QueuedConnection.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

- CatApplet: settings panel for rigctld TCP, virtual serial port, and
  DAX audio enable/disable with port configuration
- AppletPanel: persistent applet toggle states via QSettings, add CAT
  button; refactor addApplet() to restore saved visibility on startup
- MainWindow: wire up RigctlServer, RigctlPty, DaxStreamManager,
  VirtualAudioBridge; auto-start CAT/DAX based on saved settings;
  save/restore frequency, mode, connection panel collapsed state
- RadioModel: restore last frequency/mode from QSettings on reconnect
- CMakeLists.txt: add all new source files and HAL plugin subdirectory

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

- Migrate QSettings → AppSettings for connection panel collapsed state
- Add ConnectionPanel::isCollapsed() public getter
- Remove deprecated band memory restore (issue #9)
- All settings now use AppSettings XML format

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- Replace sectionHeader() with appletTitleBar() for gradient title bars
- Replace QCheckBox enables with QPushButton toggles (green active style)
- Matches STYLEGUIDE.md conventions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

DAX virtual audio needs PipeWire virtual devices to work with existing
ham radio software (WSJT-X, fldigi, FreeDV). The shared memory IPC
approach has no compatibility with standard audio apps.

Removed:
- DaxStreamManager, VirtualAudioBridge (shared memory IPC)
- macOS HAL plugin (hal-plugin/)
- DAX gain/TX gain sliders and enable button from CatApplet
- All DAX wiring from MainWindow

Kept:
- Hamlib rigctld TCP server (port 4532) + PTY virtual serial port
- CatApplet GUI with rigctld/PTY controls
- TX stuck fix (MOX gating in TransmitModel)
- DAX title bar with "coming soon" placeholder

DAX tracked in issue #15.

Co-Authored-By: pepeforg1234 <pty.11111@gmail.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

SEGV occurred in QPainter::drawLine during paintEvent when rigctld
was stopped while WSJT-X was actively polling. The crash was in
operator new (allocation failure), likely triggered by painting with
invalid geometry during a state transition.

Added early return guard when width/height are too small to render.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- Renamed "Autostart CAT/DAX with SmartSDR" to "with AetherSDR"
- Menu items are now checkable toggles, persisted via AppSettings
- When AutoStartCAT is enabled and radio connects, rigctld TCP server
  and PTY virtual serial port start automatically
- Fixes first-launch WSJT-X connection failure (server wasn't running)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CatApplet was reading cat/tcpEnable and cat/ptyEnable from old QSettings
on construction, causing the toggle buttons to fire and auto-start the
server even when Autostart CAT wasn't enabled.

- Removed per-button state persistence (tcpEnable/ptyEnable) — CAT
  auto-start is now solely controlled by the "Autostart CAT with
  AetherSDR" menu item
- Migrated port setting from QSettings cat/tcpPort to AppSettings CatTcpPort
- Removed all QSettings usage from CatApplet

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- Exclude wired actions (network, memory, spots, autostart CAT/DAX)
  from the catch-all "not implemented" handler
- Add debug logging to AutoStartCAT to verify it fires on connect
- Use saved CatTcpPort for autostart server port

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- New "Autostart rigctld with AetherSDR" menu item (TCP server)
- Existing "Autostart CAT with AetherSDR" now controls PTY only
- Both persist independently in AppSettings
- On radio connect, auto-started services sync their CatApplet
  Enable buttons to green via setTcpEnabled()/setPtyEnabled()
- Removed stale auto-start logic from CatApplet::setRigctlPty()

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

WSJT-X "Test CAT" took 46 seconds because socket->write() buffered
the dump_state response without flushing. WSJT-X waited for data
that was sitting in Qt's write buffer. Added socket->flush() after
each response write.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

socket->flush() may block if the client isn't reading. Replace with
TCP_NODELAY (LowDelayOption) on client accept to disable Nagle's
algorithm. Responses are sent immediately without buffering delays.

This fixes WSJT-X commands (band change, PTT) being queued for 42+
seconds before executing all at once.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Log every command received and response sent for diagnosing
WSJT-X connection delays. dump_state response format may need
adjustment for faster NET rigctl handshake.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>