0.13.3 — RX stats persist across idle gaps & post-decode

GUI fix

The worker emits modem_state{active:false} every time it loses the preamble — mid-burst gaps waiting for a late re-entry, brickwall, EOT, or naturally after a fully-decoded burst. The GUI was wiping the progress bar, fountain counter, σ², constellation and pilot phases on every such transition, making the operator believe the already-received blocks were lost during the gap.

Now:

• updateV2State("idle") no longer clears the visuals. The progress bar, fountain counter, σ², constellation and pilot phases stay on screen as last seen — including after session_decoded.
• session_armed clears the visuals only when a different session_id arrives (genuinely new transmission). A same-ID re-arm on the current burst keeps the existing display so a late re-entry's v2_progress events extend the bitmap instead of starting from scratch.

.deb variants

Variant	Kiosk (Pi 4 / Pi 5)	SDRplay
nbfm-modem-gui_0.13.3_arm64.deb	—	—
nbfm-modem-gui_0.13.3-sdrplay_arm64.deb	—	✓
nbfm-modem-gui_0.13.3-pi4+5_arm64.deb	✓	—
nbfm-modem-gui_0.13.3-pi4+5-sdrplay_arm64.deb	✓	✓