v0.3.15

fix(datecs-dp25): use TAB as field separator in open_fiscal (not comma)

Today's log confirms my v0.3.14 fix made operator_password=0001 flow
into the actual wire frame:
  → cmd=0x30 data=b'1,0001,1'
…but the DP-25 still NAK'd the frame. Cross-referencing the Datecs
DP-25 integrator manual + register_item already using TAB, the correct
separator for open_fiscal is TAB too. Comma is the FP-700 dialect;
DP-25's FP-55 firmware rejects it.

Ships as v0.3.15 so the next Test Print should finally open the
fiscal receipt.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>