[bmc08gt]

Implements "Including yourself" from the group-send spec (code-payments/flipcash-client-orchestrator#83). The sender can check a "You" row on Select People to split the total with themselves and keep their part.

• Select People. The sender's row comes first, under "Members" where the design's dropped Select All sat, unchecked. It is the existing member row with the sender's avatar and the "You" label the request flow already uses. "Send to N People" counts only the other members and stays disabled until one is checked.
• Split. GroupSendSplit.split takes includesSender. The sender's part is the last share, so it never takes a leftover cent, and GroupSendPlan.Pay.kept holds it. Only parts is paid: You + 4 on $5.00 is a SendPublicMultiPayment of $1.00 to each of the 4, and You + 1 is a SendPublicPayment of half. GroupSendPaymentDelegate is unchanged.
• Counting the sender. The 10 People Max cap, the "each" amount and its "", and the too-small alert all count the sender's share. isEven and smallest look at every share, the kept one included, so 5¢ between You and 2 people reads "$0.01 each" even though both paid parts are 2¢. The fixture has no vector for that case, so a unit test covers it directly.
• Confirm shows the entered total, not the amount sent. The chat bubble is unchanged.

test-vectors/group-send-split.json is copied from the orchestrator branch docs/group-send-self-share. GroupSendSplitVectorsTest now checks kept and sent and runs the 9 new includesSender vectors. ChatGroupCashLinkTest adds three cases: You + 4 pays four parts and keeps one, You counts toward the 10, and You alone sends nothing.