handlers: V2 summon ticket inventory

[Seltraeh]

handlers: V2 summon ticket inventory

Branch: split/07-summoning
Base: dev
Merge position: 07 of 13

Part of the PR #28 split. Each PR branches from dev and contains only its
own changes, so this diff is exactly one subsystem. The set is designed to be
merged in numeric order; merging all 13 reproduces PR #28 byte for byte
(verified against tree 79a4e065).

Later PRs in the series touch Handlers.hpp, GmeControllerHandlers.cpp and
UserInfo.cpp too, so once earlier ones land this branch may need a rebase.
Those conflicts are always additions on both sides — keep both. Maintainer
edits are enabled, so feel free to push the rebase directly to this branch.

Smallest PR in the series — one handler and one table.

What's included

• UnitSelectorGachaTicket (k57TdKDj) — redeem V2 typed summon tickets.
• user_summon_tickets_v2 table (migration landed in PR 3).

Note on scope

The archive-driven summoning path itself is not in this PR. GachaAction and GachaList already live on the helper layer upstream and were adopted wholesale during the merge, so they don't appear in the diff against dev at all. This only adds the typed-ticket entry point alongside them.

Verification

Redeem a ticket, confirm the count decrements and the unit is granted.