fix(schema): remove three trigram index declarations that were already dropped

[jakebromberg]

Summary

shared/database/src/schema.ts declared three GIN trigram indexes — auth_user_dj_name_trgm_idx, auth_user_name_trgm_idx, and shows_legacy_dj_name_trgm_idx — that migrations 0054 and 0065 explicitly DROP INDEX-ed. Because drizzle-kit treats schema.ts as the source of truth, every snapshot since 0055 kept carrying the entries forward — a fresh dev/test DB rebuilt from the schema would recreate the dead-weight indexes, and a future drizzle:generate against an aligned dev DB would emit a noisy catch-up migration.

Search no longer joins through auth_user or shows for dj-name lookup; reads come from flowsheet.dj_name + flowsheet_dj_name_trgm_idx.

Changes

• Removed the three index(...) declarations from schema.ts (with breadcrumb comments explaining why).
• Added 0094_drop-stale-trigram-indexes.sql catch-up migration with DROP INDEX IF EXISTS for each (no-op against environments that already applied 0054/0065).
• Updated meta/0094_snapshot.json + journal + applied-hashes.json (drizzle-kit-generated; journal when bumped to previous + 1ms per the hand-edit-when rule).
• Added tests/unit/database/schema.dropped-trigram-indexes.test.ts drift-prevention guard so a future edit can't reintroduce the declarations.

Test plan

• npm run lint
• npm run format:check
• npm run typecheck
• npm run test:unit (3155 tests pass)
• npm run lint:migrations (validator clean)
• New drift-prevention test covers all three index names and the latest snapshot.

Closes #1129

[github-actions]

Schema constraint shape report

data-shape report errored (exit 0): node:internal/modules/runmain:107 triggerUncaughtException( ^ Error ERRMODULENOTFOUND: Cannot find package 'postgres' imported from /home/runner/work/Backend-Service/Backend-Service/scripts/schema-shape-report.mjs Did you mean to import "postgres/cjs/src/index.js"? at Object.getPackageJ; manual check required