feat!: examples on donglora 1.0 async API with shared _common helpers

Rewrite all scripts against the DongLoRa Protocol v2 async Dongle surface, and extract the shared MeshCore US preset into a single module.

* _common.py: MESHCORE_US preset (910.525 MHz / BW 62.5 / SF 7 / CR 4/5 / sync 0x1424 / 20 dBm) plus small helpers, imported by every example.

* New: explore.py, which prints the device capabilities and runs a single TX + RX roundtrip for quick hardware validation.

* simple_rx.py, simple_tx.py, ping_pong.py, lora_bridge.py all switch to donglora.Dongle and the new Modulation / LoRaConfig types.

* all_commands.py removed; it was an index of the old v0.1 command enum that no longer exists after the Protocol v2 split.

* justfile: drop stale recipes that referenced removed scripts.

explore.py

@@ -0,0 +1,72 @@
+#!/usr/bin/env python3
+"""Probe a DongLoRa device: print capabilities, then TX + RX once.
+
+Configures the radio for the MeshCore US/Canada channel so the TX
+probe is audible to other MeshCore nodes on the same band.
+
+Usage:
+    python examples/explore.py [PORT]
+"""
+
+import sys
+import time
+
+import donglora as dl
+from _common import MESHCORE_US
+
+
+def describe_info(info: dl.Info) -> None:
+    chip = info.chip.name if isinstance(info.chip, dl.RadioChipId) else f"0x{info.chip:04X}"
+    print(f"  Protocol:  DongLoRa Protocol v{info.proto_major}.{info.proto_minor}")
+    print(f"  Firmware:  v{info.fw_major}.{info.fw_minor}.{info.fw_patch}")
+    print(f"  Chip:      {chip}")
+    print(f"  Freq:      {info.freq_min_hz / 1e6:.1f} - {info.freq_max_hz / 1e6:.1f} MHz")
+    print(f"  TX power:  {info.tx_power_min_dbm}..{info.tx_power_max_dbm} dBm")
+    print(f"  Max pkt:   {info.max_payload_bytes} bytes")
+    print(f"  SF range:  {info.supported_sf()}")
+    print(f"  MCU UID:   {info.mcu_uid.hex()}")
+    caps = []
+    if info.supports(dl.Capability.LORA):
+        caps.append("LoRa")
+    if info.supports(dl.Capability.FSK):
+        caps.append("FSK")
+    if info.supports(dl.Capability.CAD_BEFORE_TX):
+        caps.append("CAD")
+    print(f"  Features:  {', '.join(caps) or 'none advertised'}")
+
+
+port = sys.argv[1] if len(sys.argv) > 1 else None
+
+with dl.connect(port, config=MESHCORE_US) as d:
+    print("── GET_INFO ──")
+    describe_info(d.info)
+
+    cfg = d.config
+    print(
+        f"\n── Radio configured: {cfg.freq_hz / 1e6:.3f} MHz  "
+        f"SF{cfg.sf}  BW{cfg.bw.khz:g}kHz  "
+        f"sync=0x{cfg.sync_word:04X}  {cfg.tx_power_dbm} dBm ──"
+    )
+
+    print("\n── TX ──")
+    td = d.tx(b"hello from explore.py")
+    print(
+        f"  result={td.result.name}  airtime_us={td.airtime_us}  "
+        f"(~{td.airtime_us / 1000:.1f} ms on air)"
+    )
+
+    print("\n── RX (5 s window) ──")
+    start = time.monotonic()
+    any_rx = False
+    for pkt in d.rx(timeout=0.25):
+        any_rx = True
+        print(
+            f"  pkt: rssi={pkt.rssi_dbm:.1f}dBm snr={pkt.snr_db:.1f}dB "
+            f"len={len(pkt.data)} origin={pkt.origin.name}"
+        )
+        if time.monotonic() - start > 5:
+            break
+    if not any_rx:
+        print("  (no packets received — try pairing with ping_pong.py --role tx)")
+
+print("\nDone.")