Ports the v5 compiler layer: /opt/esp-idf-v5 + arduino-esp32 3.x
discovery (IDF5_PATH / ARDUINO_ESP32_5_PATH overridable), per-compile IDF
selection routing the family to the v5 tree, esp32c6 target support, and
the docker-runtime hardening (version-matched python venv pinned on PATH,
toolchain ordering by the tree's tools.json, user-libs component REQUIRES
for the IDF components Arduino libraries include directly). The LED_BUILTIN
fallback in the project template becomes a whitelist so non-esp32 variants
(C6 first) never hit the redefinition trap. Includes the option tests.
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