📝 Add global logger API docs

docs/api/global-log.md

@@ -0,0 +1,77 @@
+---
+name: global-log
+group: api
+category: global
+update-time: 20260512
+description: Emit a record through the shared default logger with an explicit level and optional fields.
+key-word:
+    - global
+    - log
+    - default
+    - public
+---
+
+## Global-log
+
+Emit a record through the shared default logger with an explicit level and message. This is the core global write API behind the global severity-specific shortcuts.
+
+### Interface
+
+```moonbit
+pub fn log(level : Level, message : String, fields~ : Array[Field] = []) -> Unit {}
+```
+
+#### input
+
+- `level : Level` - Severity level for the record.
+- `message : String` - Log message text.
+- `fields : Array[Field]` - Optional structured fields attached to the record.
+
+#### output
+
+- `Unit` - No return value. The record is emitted through the current shared default logger behavior.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- The function calls `default_logger().log(level, message, fields=fields)`.
+- It uses the shared console sink and the current global default threshold and target.
+- Per-call target override is not exposed by this global shortcut.
+- This helper is most useful when convenience matters more than explicit logger ownership.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need A Simple Global Logging Entry
+
+When application code wants a direct severity-controlled write:
+```moonbit
+log(Level::Info, "service started")
+```
+
+In this example, the shared default logger handles the record without requiring an explicit logger variable.
+
+#### When Attach Structured Metadata Globally
+
+When a global event should still include fields:
+```moonbit
+log(Level::Warn, "retry scheduled", fields=[field("attempt", "2")])
+```
+
+In this example, the global path still supports structured logging data.
+
+### Error Case
+
+e.g.:
+- If the level is below the current shared minimum threshold, the write is skipped.
+
+- If a custom target override is required, the explicit `Logger::log(...)` API is a better fit.
+
+### Notes
+
+1. This API is convenient but intentionally less configurable than an explicit logger value.
+
+2. Prefer explicit loggers when different subsystems need different sink or target behavior.
+