Move large repeater tables off classic ESP32 static DRAM

Classic ESP32 links into a dram0_0_seg of only 124,580 bytes: memory.ld
carves the BT controller's 0xdb5c (56,156) reservation off the 0x2c200
window before the application gets any. Three large objects dominated what
was left, and Tbeam_SX1262_repeater_observer_mqtt overran the build's 8 KiB
static reserve by 4,744 bytes.

Heap-allocate them instead, each with a defined behaviour when the
allocation fails:

- OtaContext: generalize the Companion's borrowed-storage path behind
  OTA_DYNAMIC_CONTEXT and add OTA_HEAP_CONTEXT, which allocates the context
  on first use and frees it once no transfer, apply or folder link needs it.
  A repeater is idle nearly all the time, so the workspace is usually absent.
  Exhaustion is reported to the caller and the operation declines.
- ClientACL: the client table becomes a pointer with a live capacity;
  capacity 0 refuses new clients rather than writing through a null table.
- MyMesh flood packet filters: likewise, with flood_packet_filter_slots as
  the live bound for every rule loop. At capacity 0 the node forwards
  unfiltered, and both save paths refuse to write so a stored ruleset is
  never replaced by an empty file.

Also override the Arduino SDK's weak btInUse() in simple_repeater so
initArduino() releases the BT controller memory to the heap. That grows the
runtime heap these tables now come from; it cannot recover the same
reservation from the linker's static window.

Static DRAM, classic ESP32:
  Heltec_v2_repeater                   108,332 -> 70,732
  Tbeam_SX1262_repeater_observer_mqtt  121,132 -> 83,532  (was failing)

examples/simple_repeater/main.cpp

@@ -24,6 +24,19 @@
   #include <helpers/nrf52/EthernetCLI.h>
 #endif
 
+#if defined(ESP32) && defined(CONFIG_BT_ENABLED) && !defined(BLE_PIN_CODE)
+// A repeater has no Bluetooth transport, but the Arduino SDK is built with the
+// BT controller enabled, so its memory stays reserved unless the application
+// says otherwise. initArduino() calls esp_bt_controller_mem_release() when
+// this weak hook returns false, handing that region to the heap. Note this
+// only grows the *runtime heap*: the same reservation is also carved out of
+// the linker's dram0_0_seg (0xdb5c on classic ESP32), and no runtime call can
+// give those static bytes back. It is what makes the heap-allocated tables
+// above comfortable, not a substitute for them.
+extern "C" bool btInUse();
+extern "C" bool btInUse() { return false; }
+#endif
+
 StdRNG fast_rng;
 #if MAX_RECENT_REPEATERS > 0
   #if defined(ESP32)