feat: Add Brazil Regulatory Domain (ANATEL 915MHz)

[FilipeJrd]

Motivation

• Provide a Brazil-specific 900MHz regulatory domain that satisfies ANATEL requirements (>35 FHSS channels to allow up to 30dBm) while excluding the mobile/CEL band (907.5–915 MHz).
• Avoid linear frequency arithmetic that could place channels inside the disallowed central gap by using an explicit, deterministic channel table.
• Expose the new domain to build/config tools so it can be selected at compile time.

Description

• Added a new FHSS domain entry BR915 and a domain index DOMAIN_ISM_BR_915, and introduced a static frequency lookup FHSSfreqsISM_BR_915[] with 40 explicit channel frequencies split across 902–907.5 MHz and 915–926.9 MHz, plus a selector flag FHSSuseFreqTableBR915 (changes in src/lib/FHSS/FHSS.cpp and src/lib/FHSS/FHSS.h).
• Modified FHSS selection helpers (FHSSgetInitialFreq, FHSSgetNextFreq, Gemini path) to use the BR915 lookup table when the new domain is active, falling back to existing linear interpolation for other domains (src/lib/FHSS/FHSS.h).
• Updated target validation and local compile helpers to include the new define Regulatory_Domain_ISM_BR_915 and added an example entry in src/user_defines.txt (src/include/targets.h, src/user_defines.txt).
• Added the new domain option to the Python tooling so ism_br_915 maps to the new domain index and the build flag processing sets the correct domain id (src/python/binary_configurator.py, src/python/build_flags.py).

Testing

• Ran python -m py_compile src/python/build_flags.py src/python/binary_configurator.py and the files compiled successfully.
• Ran an automated validation script that parsed FHSSfreqsISM_BR_915[] and confirmed there are 40 entries and that none fall inside 907500000–915000000 (result: count 40, in_gap False).

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Codex Task