- AdifImport.normalize_mode/2 maps ADIF MODE (and SUBMODE when present)
onto the fixed set of modes the site accepts: CW/SSB/FM/FT8/FT4/Q65.
SUBMODE takes precedence so `MODE=MFSK, SUBMODE=FT8` correctly imports
as FT8. USB/LSB/DSB all become SSB; NBFM/WFM become FM.
- Unknown modes (RTTY, PSK31, etc.) map to nil so the row still imports
— mode is optional on the submission path now.
- AdifImport.mode_mapping_reference/0 returns the user-facing list of
recognized inputs and their mappings.
- Submit page's ADIF tab renders that list in a table so users can see
upfront what will happen to their file before uploading.