Pure Python, no dependencies. Decodes raw TPDU bytes into
structured JSON: CLA bitfield, INS->name via APDU_SPEC table,
P1/P2 field breakdown, body extraction, SW name lookup.
~40 command types, 40+ SW codes, known FID notes.
database.py: _row_to_message() calls decode_message() for tpdu
messages, adding 'decoded' field to API responses.
Decoding happens at query time, not storage time — no schema
migration, all past sessions get decode retroactively.
