Fix route deletion failing due to FK constraint violations

Route deletion failed with two integrity errors:
1. route_encounters had no cascade, so SQLAlchemy tried to NULL
   the non-nullable route_id instead of deleting the rows
2. boss_battles.after_route_id referenced the route being deleted

Added cascade="all, delete-orphan" to Route.route_encounters and
nulled out boss battle after_route_id references before deletion.

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

.beans/nuzlocke-tracker-h0dr--fix-route-deletion-failing-due-to-missing-cascade.md

@@ -0,0 +1,18 @@
+---
+# nuzlocke-tracker-h0dr
+title: Fix route deletion failing due to missing cascade on route_encounters
+status: completed
+type: bug
+priority: normal
+created_at: 2026-02-14T14:19:56Z
+updated_at: 2026-02-14T14:23:10Z
+---
+
+Deleting a route returns 500 due to two FK constraint issues:
+
+1. `route_encounters.route_id` — missing cascade on the relationship (SQLAlchemy tried to NULL a NOT NULL column)
+2. `boss_battles.after_route_id` — references the route being deleted
+
+## Fix
+- Added `cascade="all, delete-orphan"` to `Route.route_encounters` relationship
+- Added `update(BossBattle).where(...).values(after_route_id=None)` before deleting the route in the delete endpoint