chore(lint): biome cleanup across services — format, sort imports, drop unused

- discord-gateway: 74 lint errors -> 0 (format, import sorting, unused
  imports/vars, dead breath var)
- backend: format + sort imports (11 warnings left: noExplicitAny)
- frontend: remove unused imports, drop dead breathing var, fix
  useExhaustiveDependencies (scroll keyed on messages), a11y biome-ignore
  for drag surface + stopPropagation container (mouse-only gestures)
- remaining warnings are false positives: index keys on static lists,
  <img> in static export (next/image unsupported), noExplicitAny

tsc --noEmit clean on all 3 services; vitest green (60+36).

services/backend/src/shared/config/index.ts

@@ -160,8 +160,6 @@ export const configSchema = z
       .default(30000)
       .describe("Timeout for individual LLM moderation calls"),
 
-
-
     // ── AI Analysis Timing ──────────────────────────────────────────────
     AI_ANALYSIS_DEBOUNCE_MS: z.coerce.number().positive().default(500),
     AI_ANALYSIS_RECOVERY_INTERVAL_MS: z.coerce