feat!: bridge on DongLoRa Protocol v2 and async client

The 1.0 bridge running on the async Dongle API from donglora-client 1.0.0 and the Protocol v2 wire format.

* Radio loop is now a tokio task, not a dedicated std::thread. Everything is async end to end.

* [radio] config schema: tx_power renamed to tx_power_dbm (plain i8, no "max" keyword), cad field removed (CAD is a per-TX flag in v1.0), default sync_word changed 0x3444 to 0x1424 to match the SX126x register encoding of MeshCore private sync byte.

* TX retry with backoff (new [tx] config section). Every TX runs through Dongle::tx_with_retry, retrying TX_DONE(CHANNEL_BUSY) and ERR(EBUSY) per PROTOCOL.md §6.10 / §C.5.5. Defaults: 3 attempts, 20-100 ms randomized backoff, doubling to 500 ms cap, 5 s per-attempt timeout. Configurable via max_attempts, backoff_min_ms, backoff_max_ms, backoff_cap_ms, backoff_multiplier, per_attempt_timeout_secs.

* TUI packet log shows retry state: in-flight retries render with a cycle marker in yellow and an N/M attempt counter, terminal TX failures render in red, post-retry success shows final attempt count.

* Stats gain tx_retries and tx_failures counters surfaced in StatsSnapshot.

* Measured airtime from TX_DONE replaces the theoretical estimate, feeding the rate limiter with the real on-air duration.

* The explicit 2 s liveness ping loop is gone. The Dongle runs a 500 ms internal keepalive, matching spec §3.4 inactivity window with 2x margin.

CHANGELOG.md

@@ -1,5 +1,48 @@
 # Changelog
 
+## [1.0.0-alpha.1] - 2026-04-21
+
+### Breaking
+
+- **Upgraded to `donglora-client` 1.0.0-alpha.1 (DongLoRa Protocol v2 wire protocol).**
+  Wire-incompatible with 0.x firmware. Connect/config/TX/RX all go through
+  the new async `Dongle` API.
+- **Radio loop is now a tokio task**, not a dedicated `std::thread`.
+  Everything is async end-to-end.
+- **`[radio]` config schema changes:**
+  - `tx_power` renamed to `tx_power_dbm` and is now a plain `i8` (no
+    `"max"` keyword — v1.0 exposes a concrete dBm range via `GET_INFO`).
+  - `cad` field removed — CAD is a per-TX flag in v1.0, not a config
+    property. The `[tx]` section's `skip_cad` (default false) controls it.
+  - Default `sync_word` changed `0x3444` → `0x1424` to match the
+    `SX126x` register encoding of `MeshCore`'s private sync byte
+    (`RADIOLIB_SX126X_SYNC_WORD_PRIVATE`).
+
+### Added
+
+- **TX retry with backoff (new `[tx]` config section).** Every TX now
+  runs through `Dongle::tx_with_retry`, which retries `TX_DONE(CHANNEL_BUSY)`
+  and `ERR(EBUSY)` per spec `PROTOCOL.md §6.10` / §C.5.5. Defaults: 3
+  attempts, randomized 20–100 ms backoff, doubling up to 500 ms cap,
+  5 s per-attempt timeout. Configurable via `[tx]` keys `max_attempts`,
+  `backoff_min_ms`, `backoff_max_ms`, `backoff_cap_ms`,
+  `backoff_multiplier`, `per_attempt_timeout_secs`.
+- **TUI packet log shows retry state.** In-flight retries render with a
+  `↻` marker in yellow and an `N/M` attempt counter. Terminal TX failures
+  render in red with `✗`. Post-retry success shows the final attempt count
+  (`OK 2/3`).
+- **Stats: `tx_retries` and `tx_failures` counters.** Lifetime totals,
+  surfaced in the `StatsSnapshot`.
+- **Measured airtime** from `TX_DONE` is now reported instead of a
+  theoretical estimate, feeding the rate limiter with the real on-air
+  duration.
+
+### Removed
+
+- The explicit 2-second liveness ping loop in the radio thread. The
+  `Dongle` now runs a 500 ms keepalive task internally, matching spec
+  §3.4's 1 s inactivity window with 2× margin.
+
 ## [0.3.1] - 2026-04-07
 
 ### Fixed