TabRe Red Packet

A member puts points aside on a topic and everyone else grabs a random share (Discuz's 红包).

On a topic without a packet, the author (or a moderator) gets an Open a red packet form under the replies:
a total and a number of shares. The points leave the author's balance at once.
Every other member who opens the topic sees the packet card in the topic header and a Grab a share button; one
share per member. The split is random but always leaves at least one point for every share still open.
When the shares run out the card says so. A packet nobody finishes is refunded to its author by a scheduled job
after expire_days.

Every movement goes through the ledger: tabre_redpacket_out, tabre_redpacket_in, tabre_redpacket_back.

Piece	Where
Packets	`plugin_tabre_redpacket_packets`
Claims	`plugin_tabre_redpacket_claims` (unique on packet + member)
Routes	`POST /t/{id}/redpacket`, `POST /t/{id}/redpacket/claim`

Enabled, Smallest total, Largest total, Most shares, Refund after (days).

One packet per topic; the author cannot grab their own.
The claiming happens inside a transaction and re-reads the packet row, so two people clicking at once can never take
the same share.

Disable stops new packets and hiding the card. Uninstall drops both tables.