feat: share reset windows and deterministic stock logic

[ggmolly]

Summary

• Standardizes shop reset windows with shared daily/monthly helpers so shop state aligns to region reset boundaries.
• Makes guild shop stock generation deterministic per commander and reset window while preserving weighted pool behavior from config data.
• Implements monthly template rotation for month shop and medal shop flows so core/prototype/medal catalogs rotate by month template id.
• Extends guild manual refresh handling to support refresh limits and cost ladders from guild settings.

Changes

• Added internal/shopreset shared utilities for reset windows and deterministic seed derivation.
• Updated guild/arena/medal shop services to consume shared reset windows instead of fixed UTC-only day math.
• Updated month shop handlers to select the active template entry by current month and use reset-aware month keys for purchase counts.
• Updated guild shop handler to apply refresh limit/cost progression and pass refresh counters through refresh operations.
• Added and updated shop-focused tests for deterministic selection behavior, reset semantics, month-template selection, and guild refresh ladders.

[chatgpt-codex-connector]

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