…odals (#2785)

## Summary

PR #2771 (merged today) added user-facing dialogs for M-prefix radio
messages. In practice the radio sends an **Info-severity** M-message on
every client connect/disconnect (\"Client connected from IP …\" etc.) —
routine multi-client notices that SmartSDR silently logs. AetherSDR was
popping a modal warning dialog on every connect as a result.

The fix extracts the severity bits that FlexLib documents but
AetherSDR's parser was discarding, then surfaces messages appropriately
by severity.

## Root cause

FlexLib's wire format
([Radio.cs:4498-4516](https://github.com/FlexRadioSystems/FlexLib/blob/main/FlexLib/Radio.cs#L4498))
encodes severity in bits 24-25 of the M-message number:

\`\`\`
M<8-hex-digits>|<text>
        └── (num >> 24) & 0x3 → Info=0, Warning=1, Error=2, Fatal=3
\`\`\`

AetherSDR's \`CommandParser\` was extracting the handle as a single hex
value but **discarding the severity bits**. PR #2771's MainWindow
handler then treated all M-messages identically as
\`QMessageBox::warning\`.

## What changes

- \`CommandParser\`: new \`MessageSeverity\` enum + \`severity\` field
on \`ParsedMessage\`; \`'M':\` case now extracts \`(handle >> 24) &
0x3\` into it
- \`RadioModel::radioMessageReceived\` signal extended to \`(QString,
MessageSeverity)\`
- \`RadioModel::onMessageReceived\` logs at the matching protocol level
(\`qCInfo\` / \`qCWarning\` / \`qCCritical\`) — log path and UI path now
both switch on the same enum so they can't disagree
- \`MainWindow::onRadioMessage\` switches on severity:

| Severity | Behavior |
|---|---|
| **Info** | \`statusBar()->showMessage(text, 5000)\` — 5-second toast,
no modal |
| **Warning** | \`QMessageBox::warning\` (PR #2771's intent preserved) |
| **Error** | \`QMessageBox::critical\` with \"Radio — Error\" title |
| **Fatal** | \`QMessageBox::critical\` with \"Radio — Fatal\" title |

## Behavior changes

- \"Client connected from IP …\" → status-bar toast (was modal popup) ✅
- \"Client disconnected from IP …\" → status-bar toast (was modal popup)
✅
- FreeDV mode-conflict warning from #2771 — unchanged, still modal ✅
- Future ATU / interlock / calibration errors — modal with
\"Error\"/\"Fatal\" title prefix instead of \"Radio\" generic

## Test plan

- [x] Local build clean (402/402 link, only pre-existing warnings)
- [x] Connect to FLEX-8400 — IP notice appears in status bar for 5
seconds, no modal interrupts connection flow. **Confirmed by @ten9876.**
- [ ] Trigger a Warning-severity M-message (e.g. set two slices to FDVU
when FreeDV is running) — modal warning still appears
- [ ] No regression in other M-message consumers (none exist in current
codebase per grep)

## Files

| File | Change |
|---|---|
| \`src/core/CommandParser.h\` | \`MessageSeverity\` enum +
\`ParsedMessage::severity\` field + protocol-format comment refresh |
| \`src/core/CommandParser.cpp\` | Extract severity bits in the \`'M':\`
case |
| \`src/models/RadioModel.h\` | Signal signature + \`CommandParser.h\`
include |
| \`src/models/RadioModel.cpp\` | Switch on severity for log level; emit
with severity |
| \`src/gui/MainWindow.h\` | Slot signature + \`CommandParser.h\`
include |
| \`src/gui/MainWindow.cpp\` | Switch on severity for log + dialog/toast
|

Net: **83 insertions / 16 deletions** across 6 files.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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