Osmosis neo2-test-v1.3.0

Test build for the DJI Neo 2, off the drones branch.

Why this build exists

A Neo 2 gets as far as the datalink and then stops at the 0x51 session-open:

handshake OK on udp/9003
session=0x7b46 channel=0x87b8
no drone serial seen in a beacon — cannot open the session
drone list FAILED ... rx [NOTHING — link silent]

The session-open has to echo the aircraft's own serial back at it, read out of its 0x51/0x13
beacon. No serial, no session, and every command is ignored.

What changed

• The serial length is measured, not assumed. It was fixed at 20 characters, which is a
  Mavic 3's and nothing more principled — any aircraft with a different length would find the
  tag, fail the fixed-width check, and report "no serial".
• A failed open now says what it saw, so the next run can tell a drone that never beacons
  from one whose beacon we fail to parse. Those need completely different fixes.

⚠️ Expect one pairing prompt

This build gives every install its own pairing identity instead of a shared constant. An
aircraft that had approved an earlier Osmosis build will treat this as a new app and ask for
confirmation: the lights will flash and you hold the power button for ~2 seconds (three
quick presses on a Mini 3). One time only — silent after that. This is expected, not a fault.

What to send back

Turn Save logs on before connecting. The useful line comes straight after
no drone serial seen in a beacon:

• 0x51 inner cmds seen: NONE — the aircraft never beacons; the open needs a different trigger.
• a 0x51/0x13 beacon DID arrive but carried no readable serial — payload … — it beacons in a
  shape we do not parse, and the hex says which.
• drone serial XXXX (N chars) — the length fix was the whole problem and it should just work.

Also worth noting: last run the AP dropped ~16 s after joining, so tap the drone and browse
straight away rather than letting it sit.

Also in here

Everything on drones: Mavic 3 offload end to end, the pairing-identity work, the delete
handle fix, and the Osmo Action index-list decoder. The Action 5 Pro, Action 6, Nano and
Pocket 3 all passed in the same tester session that produced the Neo 2 log.