port to ESP-IDF 6.0 and open62541 v1.5.4

[diplfranzhoepfinger]

feat: port to ESP-IDF 6.0 and open62541 v1.5.4, minimal NS0 build

• Update open62541 build to freertos-lwip architecture (renamed from
  freertosLWIP), providing FreeRTOS stub and no_install.cmake to satisfy
  CMake configure without a host FreeRTOS source tree
• Switch BUILD_COMMAND to open62541-amalgamation target
• Add patch_config.cmake to disable UA_HAS_GETIFADDR in generated
  config.h (not available on FreeRTOS/ESP32)
• Add compat_includes/ wrappers for FreeRTOS.h and task.h (IDF 5+
  requires freertos/ prefix)
• Suppress all warnings on generated open62541.c (third-party file)
• Add gethostname() shim to custom_getaddrinfo.c
• Switch UA_NAMESPACE_ZERO from FULL + hand-maintained nodes_blacklist.txt
  to REDUCED: open62541's own curated minimal NS0 (Opc.Ua.NodeSet2.Reduced.xml
  plus per-feature Minimal.xml nodesets), gated by UA_ENABLE_ flags. The
  blacklist approach kept breaking whenever a blacklisted node was still
  transitively referenced (DataType, HasTypeDefinition, reference type
  lookups) by an active node. nodes_blacklist.txt is now unused and removed.
• Disable UA_ENABLE_DIAGNOSTICS, UA_ENABLE_HISTORIZING, UA_ENABLE_PUBSUB,
  UA_ENABLE_DA, UA_ENABLE_SUBSCRIPTIONS_EVENTS, UA_ENABLE_JSON_ENCODING,
  UA_ENABLE_XML_ENCODING and UA_ENABLE_STATUSCODE_DESCRIPTIONS to shrink
  the build; keep UA_ENABLE_DISCOVERY/_MULTICAST=MDNSD (used by main.c's
  mDNS setup) and leave UA_ENABLE_TYPEDESCRIPTION / UA_ENABLE_DATATYPES_ALL
  at their defaults (ON) since open62541 v1.5.4's security/GDS code and
  structure-description parsing reference types that don't compile with
  either one turned off
• Migrate main.c APIs for IDF 5+/6:
  • UA_String_deleteMembers/UA_LocalizedText_deleteMembers → _clear
  • tcpip_adapter → esp_netif
  • spi_flash_init/get_chip_size → esp_flash_get_size
  • sntp_* → esp_sntp_*
  • esp_task_wdt_init → esp_task_wdt_config_t struct
  • UA_ServerConfig.customHostname → serverUrls
  • UA_ARCHITECTURE_FREERTOSLWIP guard moved after open62541.h include
• Add CONFIG_ETHERNET_HELPER_CUSTOM_HOSTNAME to sdkconfig.defaults
• Add spi_flash to main component REQUIRES
• Binary size drops from ~2.9 MB (98% of the 3 MB factory partition) to
  ~1.1 MB (63% free); factory partition size left at 3 MB for headroom

Co-Authored-By: Claude Sonnet 4.6 noreply@anthropic.com
Co-Authored-By: Claude Sonnet 5 noreply@anthropic.com

[diplfranzhoepfinger]

Switch UA_NAMESPACE_ZERO from FULL + hand-maintained nodes_blacklist.txt
to REDUCED: --> this is the Main change here.