Add ISO 15693 16-slot inventory with anti-collision tree-walking, reachable via 'hf 15 reader --all'; single-tag reading stays the default. The firmware steps the 16 slots with EOF markers and flags 'signal but no decode' slots as collision hints; the client walks the UID mask tree, validates CRC per slot to confirm real collisions, and dedups discovered tags. Single-tag reading (default) and 16-slot inventory (--all) both run under hf 15 reader.