feat(ui): mesh header "Flash LoRa" button opens the in-app flash flow

Replaces the external flasher.meshcore.co.uk link with a button that
opens the global device-setup modal directly at its flash step, via a
new manual entry point in the mesh store (flashFlowPath). Manual opens
target the connected radio (else the first detected stick), skip the
read-only probe — the port is held by the live session and a second tty
opener corrupts it; the backend flash job stops the listener itself —
and close the modal instead of stepping back to the detection screen.
Button is disabled with a hint when no radio is present.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

neode-ui/src/views/mesh/mesh-styles.css

@@ -28,6 +28,7 @@
 .mesh-subtitle { color: rgba(255, 255, 255, 0.5); font-size: 0.85rem; margin: 2px 0 0; display: flex; align-items: center; gap: 8px; }
 .mesh-subtitle-badge { font-size: 0.65rem; font-weight: 600; color: #4ade80; background: rgba(74, 222, 128, 0.12); padding: 1px 6px; border-radius: 4px; text-transform: uppercase; letter-spacing: 0.5px; }
 .mesh-flasher-btn { display: inline-flex; align-items: center; gap: 0; padding: 8px 16px; font-size: 0.9rem; text-decoration: none; white-space: nowrap; flex-shrink: 0; }
+.mesh-flasher-btn:disabled { opacity: 0.45; cursor: not-allowed; }
 .mesh-flasher-sep { margin: 0 8px; color: rgba(255, 255, 255, 0.2); }
 .mesh-error { color: #ef4444; font-size: 0.85rem; padding: 8px 12px; background: rgba(239, 68, 68, 0.1); border-radius: 8px; border: 1px solid rgba(239, 68, 68, 0.2); flex-shrink: 0; }
 .mesh-columns { display: flex; gap: 16px; flex: 1; min-height: 0; overflow: hidden; }