📝 Add filter predicate API docs

docs/api/not.md

@@ -0,0 +1,76 @@
+---
+name: not
+group: api
+category: filtering
+update-time: 20260512
+description: Create a reusable record predicate that negates another predicate.
+key-word:
+    - negate
+    - filter
+    - predicate
+    - public
+---
+
+## Not
+
+Create a `RecordPredicate` that returns the logical inverse of another predicate. This helper is the standard way to express exclusion rules without rewriting predicate bodies.
+
+### Interface
+
+```moonbit
+pub fn not_(predicate : RecordPredicate) -> RecordPredicate {}
+```
+
+#### input
+
+- `predicate : RecordPredicate` - Existing predicate to invert.
+
+#### output
+
+- `RecordPredicate` - Predicate that returns `true` when the original predicate returns `false`.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- `not_(...)` delegates evaluation to the original predicate and flips the boolean result.
+- It does not change the record or short-circuit upstream logic outside the wrapped predicate.
+- This helper is useful for excluding known noisy targets, fields, or message patterns.
+- It composes well with `all_of(...)` and `any_of(...)` for more expressive routing rules.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Exclude One Target Prefix
+
+When everything except one noisy subsystem should pass:
+```moonbit
+let logger = Logger::new(console_sink())
+  .with_filter(not_(target_has_prefix("debug.spam")))
+```
+
+In this example, records under `debug.spam...` are filtered out.
+
+#### When Invert A Field Match
+
+When one tenant should be excluded from a shared stream:
+```moonbit
+let predicate = not_(field_equals("tenant", "internal"))
+```
+
+In this example, all non-internal tenant records continue through the filter.
+
+### Error Case
+
+e.g.:
+- If the wrapped predicate always returns `true`, the negated predicate always returns `false`.
+
+- If the wrapped predicate is too broad, the inversion may unintentionally admit unrelated records.
+
+### Notes
+
+1. Prefer `not_(...)` over duplicating inverse logic inline because the intent is easier to read.
+
+2. Negation is most maintainable when the wrapped predicate is itself narrow and well named.
+