server roles, event loops, companion transports, storage and prefs.json

Server roles (slice 7)
- CommonCLI split into upstream's shape; region CLI moved into CommonCLI;
  ClientACL, RegionMap, TransportKeyStore and both server meshes in
  upstream shape over an Arduino compat shim (helpers/compat: Arduino.h,
  Stream/Print, Serial, SHA256, FILESYSTEM/File over Zephyr fs)
- room server processAck port; `get acl` prints as upstream
- room: default name Room-XXXX, display/input rotation, live radio UI refresh

Event loops (slice 7b)
- repeater and room server share server_main_common with a ServerRole
  descriptor; shared event bits in src/mesh_events.h
- room server deadline-driven (idle wakes 2.2/s -> 0.08/s); companion
  loop() runs on housekeeping (closes the lazy contact-flush gap)
- `get loop.wakes` in debug builds (CONFIG_ZEPHCORE_LOOP_WAKE_STATS)

Companion transports and WiFi (slice 8)
- upstream MultiSerialInterface: BLE, USB/UART and TCP are each a
  BaseSerialInterface, every connected transport gets every frame;
  CompanionSerial holds a lossless reply; shared frame_txq for BLE/TCP
- SerialCompanionTransport and LinuxTCPTransport replaced by
  TcpCompanionTransport; ZephyrBLE split (gatt layout, DFU)
- WiFi companion (upstream wifi.ssid/pwd/enabled CLI, TCP port 5000) on
  boards declaring `capabilities: wifi` in zephcore.yml: the PSRAM
  ESP32-S3 boards, plus Heltec V3 (140 contacts), Wireless Tracker (130)
  and both C6 boards (280); ESP32-S3 without PSRAM gets bounded WiFi
  buffers and a measured 72 KB heap; PSRAM boards' internal heap 72 KB
- TCP queues: own depth (ZEPHCORE_TCP_QUEUE_SIZE=8), RX waits instead
  of dropping
- RAM: companion ClientACL dropped; main/BT-TX/TCP stacks sized from
  measured peaks (-7 KB nRF companions, -9 KB ESP32 companions)
- ESP32 WiFi stopped working under ~200 frames/s unicast. Fixed by:
  patches/zephyr/0017 never block the WiFi task in the RX callback;
  patches/zephyr/0018 lock shared_multi_heap (heap corruption with the
  WiFi heap in PSRAM); patches/modules/hal_espressif/0001 backport of
  hal_espressif af97fb02df (PSRAM realloc)

Storage and prefs (slice 9)
- prefs are now prefs.json through upstream's ConfigSerializer (ported
  verbatim), with upstream's key names for shared fields and ZephCore's
  own under "zc"; on first boot the binary new_prefs / repeater prefs is
  migrated and kept, so a downgrade still boots with the old settings
- helpers/PrefsCodec: both legacy binary layouts (companion 272 B,
  server 311 B) as Zephyr-free codecs; sanitizeNodePrefs is the only
  validator
- fix: server prefs could be replaced by a truncated file when a write
  failed; identity, prefs and channel writes go through one checked
  atomic replace (ZephyrFsUtil)
- fix: a corrupt cad_auto byte turned adaptive CAD off instead of the
  default on
- fix: a deliberate 300 s GPS duty on a repeater was rewritten to 48 h
  on every boot (that migration now runs on legacy files only)
- one identity loader for all roles (IdentityFile); an unusable key
  file is always parked as .bad before regenerating
- server store no longer stamps repeater defaults on room server and
  observer; companion first-boot volume policy moved into the store
  (adoptVolume)
- ZephyrDataStore 1435 -> ~850 lines

zephcore/app/ObserverMesh.cpp

@@ -11,7 +11,6 @@
 #include <adapters/rng/ZephyrRNG.h>   /* generateFirstBootIdentity (hardened keygen) */
 #include <helpers/MeshcoreJson.h>
 
-#include <zephyr/fs/fs.h>
 #include <zephyr/logging/log.h>
 LOG_MODULE_REGISTER(zephcore_observer, CONFIG_ZEPHCORE_OBSERVER_LOG_LEVEL);
 
@@ -58,32 +57,10 @@ void ObserverMesh::begin(RepeaterDataStore *store, struct ObserverCreds *creds)
 	_prefs.tx_power_dbm = 0;   /* observer never TXes anyway */
 	/* freq=869.618, bw=62.5, sf=7 already set by initNodePrefs */
 
-	/* First boot has to be detected BEFORE loadPrefs(): the store is shared
-	 * with the repeater and its no-file branch re-runs initNodePrefs(), applies
-	 * *repeater* defaults over whatever the caller passed in, saves them, and
-	 * returns true.  So the observer values set above are silently discarded on
-	 * a fresh unit and there is no return code that says so.  Probing for the
-	 * file is the only observer-local way to tell — the alternative, changing
-	 * the no-file branch, would alter repeater and room-server behaviour. */
-	char prefs_path[64];
-	struct fs_dirent prefs_ent;
-	snprintf(prefs_path, sizeof(prefs_path), "%s/prefs", _store->getBasePath());
-	const bool first_boot = (fs_stat(prefs_path, &prefs_ent) < 0);
-
-	/* Load persisted prefs (overrides defaults with saved values) */
+	/* Persisted prefs override the defaults above; on a fresh unit the store
+	 * saves these defaults as they are. */
 	_store->loadPrefs(_prefs);
 
-	if (first_boot) {
-		/* Re-apply the observer defaults the shared no-file branch overwrote,
-		 * then persist them so this runs exactly once.  Only the prefs file is
-		 * rewritten — obs_creds (WiFi/MQTT/IATA/lat/lon) is a separate file and
-		 * is never touched here. */
-		_prefs.cr           = 5;
-		_prefs.tx_power_dbm = 0;
-		_store->savePrefs(_prefs);
-		LOG_INF("First boot — saved observer prefs defaults");
-	}
-
 	/* Load or generate node identity.
 	 *
 	 * Use ZephyrRNG::generateFirstBootIdentity — the SAME hardened path the