📝 Add global logger API docs

docs/api/default-logger.md

@@ -0,0 +1,75 @@
+---
+name: default-logger
+group: api
+category: global
+update-time: 20260512
+description: Create the shared console-backed logger value used by the global logging helpers.
+key-word:
+    - global
+    - logger
+    - default
+    - public
+---
+
+## Default-logger
+
+Create a `Logger[ConsoleSink]` from the current shared default global configuration. This is the logger value used internally by the global helper functions such as `log(...)`, `info(...)`, and `error(...)`.
+
+### Interface
+
+```moonbit
+pub fn default_logger() -> Logger[ConsoleSink] {}
+```
+
+#### output
+
+- `Logger[ConsoleSink]` - Logger built from the shared console sink, current default minimum level, and current default target.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- The returned logger is built from `default_console_sink`, `default_min_level_ref`, and `default_target_ref`.
+- Each call reflects the current shared configuration at that moment.
+- The logger writes to the standard console sink path.
+- This helper is useful when you want the same baseline behavior as the global shortcuts but still need the explicit `Logger` object for chaining or inspection.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Start From Global Defaults But Keep A Logger Value
+
+When code wants the default console path with later composition:
+```moonbit
+let logger = default_logger().with_timestamp()
+logger.info("service started")
+```
+
+In this example, the logger starts from global defaults and then gains extra instance-level behavior.
+
+#### When Inspect Current Shared Behavior
+
+When code should branch using the same threshold as global helpers:
+```moonbit
+let logger = default_logger()
+if logger.is_enabled(Level::Debug) {
+  logger.debug("debug path active")
+}
+```
+
+In this example, the explicit logger mirrors the same level gate used by global shortcut calls.
+
+### Error Case
+
+e.g.:
+- If the shared default target is empty, the returned logger is still valid and simply uses an empty target.
+
+- Changes made later through `set_default_min_level(...)` or `set_default_target(...)` do not mutate an already-stored logger value.
+
+### Notes
+
+1. This helper returns a normal `Logger`, so further chaining is available.
+
+2. It is the bridge between the simple global API and the explicit typed logger workflow.
+