📝 Document logger config presets

docs/api/json-console.md

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+---
+name: json-console
+group: api
+category: config
+update-time: 20260520
+description: Create a logger config preset for the built-in JSON console sink.
+key-word:
+    - preset
+    - json
+    - console
+    - public
+---
+
+## Json-console
+
+Create a `LoggerConfig` preset for structured JSON output on the console. This preset is intended for config-driven logging pipelines that want machine-readable terminal output.
+
+### Interface
+
+```moonbit
+pub fn json_console(
+  min_level~ : Level = Level::Info,
+  target~ : String = "",
+  timestamp~ : Bool = false,
+) -> LoggerConfig {
+```
+
+#### input
+
+- `min_level : Level` - Minimum enabled level for the preset.
+- `target : String` - Default target stored in the returned config.
+- `timestamp : Bool` - Whether emitted records should include timestamps.
+
+#### output
+
+- `LoggerConfig` - Config using `SinkKind::JsonConsole` with no queue wrapper by default.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- This preset always returns `sink.kind=SinkKind::JsonConsole`.
+- `queue=None` by default, so JSON records are not buffered unless `with_queue(...)` is added later.
+- The preset does not carry file-only fields such as `path` or `rotation` in a meaningful way because the sink kind is not file-based.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Structured Console Output
+
+When logs should be easy to collect or parse from stdout:
+```moonbit
+let config = json_console(min_level=Level::Info, target="api", timestamp=true)
+let logger = build_logger(config)
+```
+
+In this example, records are emitted through the JSON console sink.
+
+And timestamps are enabled at the top-level logger config.
+
+### Error Case
+
+e.g.:
+- If `target` is empty, the preset still returns a valid config.
+
+- If you need file rotation or file paths, this preset is the wrong sink shape and should be replaced with `file(...)`.
+
+### Notes
+
+1. Use this preset when downstream tooling expects structured console logs.
+
+2. `with_file_rotation(...)` does not change this preset because it only applies to file configs.