The ON CONFLICT upsert referenced unqualified "bought" which PostgreSQL
rejected as ambiguous, and the table lacked the UNIQUE constraint needed
for ON CONFLICT. Adds a unique index on (character_id, shop_item_id) via
migration 0003 and qualifies the column as shop_items_bought.bought.
Move scan loops from handlers into repository methods so that interfaces
return typed slices instead of leaking database cursors. This fixes
resource leaks (7 of 12 call sites never closed rows) and makes all
12 methods mockable for unit tests.
Affected repos: CafeRepo, ShopRepo, EventRepo, RengokuRepo, DivaRepo,
ScenarioRepo, MiscRepo, MercenaryRepo. New structs: DivaEvent,
MercenaryLoan, GuildHuntCatUsage. EventRepo.GetEventQuests left as-is
(requires broader Server refactor).
Move 22 raw SQL queries from 4 handler files into dedicated repository
structs, continuing the repository extraction pattern. Achievement
insert uses ON CONFLICT DO NOTHING to eliminate check-then-insert race,
and IncrementScore validates the column index to prevent SQL injection.
