add-setting-env

Define the variable in packages/env/src/<domain>.ts using createEnv from @t3-oss/env-core with a zod schema, then wire it through the server config type, global config assembly, and user store merge. Finish by documenting it in .env.example and the environment-variables docs.

The precedence is User Custom > Server Env Var > Hardcoded Default. A value explicitly set by the user always wins; the environment variable only supplies the default when the user has not customized the setting.

Validation uses @t3-oss/env-core's createEnv combined with zod schemas, for example z.coerce.number().min(1).max(20).optional(). The runtimeEnv field maps process.env values explicitly.

Yes, new domains require adding a field to GlobalServerConfig in packages/types/src/serverConfig.ts, preferably reusing existing types from packages/types/src/user/settings via PartialDeep. Existing domains only need the env definition and config wiring.

Update .env.example with a commented example including range and default, plus both docs/self-hosting/environment-variables/basic.mdx (English) and basic.zh-CN.mdx (Chinese) to keep bilingual docs in sync.