Revert "feat(topics): compute topic overviews and topic pages on the server"

This reverts commit cc04e0944d.

src/lib/openapi/error-codes.ts

@@ -452,7 +452,6 @@ export const ERROR_CODE_CATALOGUE: Readonly<Record<string, readonly string[]>> =
       "tokens.measurements.ceiling_reached",
       "tokens.workouts.ceiling_reached",
     ],
-    topics: ["topics.not_available", "topics.not_found", "topics.preview_off"],
     vaccination: [
       "vaccination.booster-invalid",
       "vaccination.booster-no-antigen",