Add Pinwheel Clause support for zone-based encounters in route groups

Allows each sub-zone within a route group to have its own independent
encounter when the Pinwheel Clause rule is enabled (default on), instead
of the entire group sharing a single encounter.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.beans/nuzlocke-tracker-i08l--implement-pinwheel-clause-support.md

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+---
+# nuzlocke-tracker-i08l
+title: Implement Pinwheel Clause support
+status: completed
+type: feature
+priority: normal
+created_at: 2026-02-07T19:18:34Z
+updated_at: 2026-02-07T19:21:45Z
+---
+
+Add pinwheel_zone column to routes, pinwheelClause toggle to NuzlockeRules, zone-aware encounter locking on frontend and backend.
+
+## Checklist
+- [x] Alembic migration for pinwheel_zone column
+- [x] SQLAlchemy model update
+- [x] Pydantic schema updates
+- [x] Route list API helper update
+- [x] Encounter creation API zone-aware sibling check
+- [x] Seed loader update
+- [x] Seed data for Pinwheel Forest zones
+- [x] NuzlockeRules per-run toggle
+- [x] Frontend types (game.ts, admin.ts)
+- [x] Admin route form pinwheelZone input
+- [x] Encounter page zone-aware locking, counts, and filtering
+- [x] getZoneEncounters helper