Require esp-idf 5.3.x with a clear error

[jmarler]

problem

main/idf_component.yml declares idf: '>=5.3,<5.4', but nothing enforces it. The Espressif installer (EIM) now defaults to 6.0.x, so a fresh setup builds against an unsupported version and fails several minutes into compilation with two confusing errors:

fatal error: driver/uart.h: No such file or directory
fatal error: mbedtls/rsa.h: No such file or directory

Neither message points at the real cause. The mbedtls one is actively misleading, because ESP-IDF's hint locates the header inside OpenThread's vendored copy of mbedtls and suggests adding an include directory, which cannot work.

Both are IDF 6.0 breaking changes:

• the driver umbrella component no longer re-exports UART, so REQUIRES driver does not supply driver/uart.h
• IDF 6.0 ships mbedTLS 4.x, which moved the legacy crypto modules into TF-PSA-Crypto and dropped the public headers. main/piv.c uses mbedtls_rsa_context and mbedtls_rsa_private, and main/touch_pin_hid.c uses mbedtls_aes_crypt_ctr, so no CMake change can fix it.

Reported in #8, where it was understandably attributed to the macOS version rather than the toolchain.

changes

• firmware/tiny_touch_smartcard/CMakeLists.txt: fail at configure time with install instructions when IDF is not 5.3.x. The check is skipped if IDF_VERSION_MAJOR is undefined, so it cannot break builds on toolchains that do not expose it.
• tinytouch: run_idf() now checks idf.py --version once before running anything, and reports the same guidance. This matters because run_idf() prefers whatever idf.py is on PATH, then $IDF_PATH/export.sh, so an EIM install silently supplies 6.0.x.
• main/CMakeLists.txt: add esp_driver_uart to PRIV_REQUIRES. Not required on 5.3, but it is the correct explicit dependency for driver/uart.h.
• README.md: state the required version in the build section, with install steps and a note to clear build/, sdkconfig, and dependencies.lock after a failed 6.0 attempt. A stale dependencies.lock records the old IDF version and keeps the build broken.

testing

• Verified the Python guard against idf.py --version reporting 6.0.2, 5.3.3, 5.4.1, and unparseable output. Rejects with actionable text on mismatch, accepts 5.3.x, and falls through quietly when the version cannot be parsed.
• Built successfully on ESP-IDF 5.3.3 for ESP32-S3 with the guard in place.

notes

This keeps the project on 5.3.x rather than porting to IDF 6.0. Supporting 6.0 means moving piv.c and touch_pin_hid.c to the PSA crypto API, and the raw RSA operation behind PIV general authenticate has no clean PSA equivalent. That felt like a separate decision, so this PR just makes the current requirement explicit and fast to diagnose.

Closes #8