fix(monsters): finish deleting experienceReward, column included

Design ruling R7 abolishes XP as a concept and says the column goes with
it, but no task in the plan actually dropped it -- the plan only dropped
characters.experience and combat_rewards.experience_granted. Task 9
removed experienceReward from the seed literals, leaving
monster_definitions.experience_reward as a NOT NULL column with no
default that nothing supplies. The first monster insert against a real
database would have failed on a constraint violation.

No suite here could have caught it: none of them connect to Postgres.

Drops the column in the slice migration (which has never been run, so
amending it in place is correct rather than stacking a second one),
removes the entity field, and clears the three test fixtures that still
set it. silver_min/silver_max deliberately stay -- spec 15 keeps a
direct currency drop available as a lore-valid exception, and XP has no
such carve-out.

Also retargets the seed idempotency test off renown: 1, which is the
seed's own default and so could not distinguish "preserved" from
"reset to default".

NOTE ON SCOPE: this commit also absorbs a Prettier reformatting pass
that was already sitting uncommitted in the working tree, which is why
it touches ~59 files. That churn is purely cosmetic line-rewrapping --
verified by inspection, and the suite is green at 267/267 with the build
at exactly the 3 expected errors owned by Tasks 10 and 11. The repo is
not Prettier-clean at baseline (119 files still flagged), so this was a
partial run by an earlier step, not a deliberate repo-wide format.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

apps/api/src/monsters/entities/monster-definition.entity.ts

@@ -34,9 +34,6 @@ export class MonsterDefinition {
   @Column({ name: 'armor', type: 'integer' })
   armor!: number;
 
-  @Column({ name: 'experience_reward', type: 'integer' })
-  experienceReward!: number;
-
   @Column({ name: 'silver_min', type: 'integer' })
   silverMin!: number;