✨ Finalize and document the public API surface

Export the matcher builder types from the barrel and rename them off the
internal Strict/Widening suffixes, so the type a factory returns is
nameable: PrimitiveUnionMatcher/W, TaggedUnionMatcher/W, and the
tagged-union factory types. Add TSDoc to every public symbol — the
declarations carry it into the published package — and pin the exported
names in src/index.test.ts.

Document the API in README and record the surface decision (and the
rejected matcher-shared export) in development/library.md.

src/index.ts

@@ -1,8 +1,26 @@
+/**
+ * The public entry point of `tiny-pattern-ts`.
+ *
+ * Exports the four matcher factories and the builder types they return.
+ * Everything else in `src/` is an implementation detail.
+ *
+ * @module
+ */
 export {
     getPrimitiveUnionMatcher,
     getPrimitiveUnionMatcherW,
 } from "./primitive-union.ts";
+export type {
+    PrimitiveUnionMatcher,
+    PrimitiveUnionMatcherW,
+} from "./primitive-union.ts";
 export {
     getTaggedUnionMatcher,
     getTaggedUnionMatcherW,
 } from "./tagged-union.ts";
+export type {
+    TaggedUnionMatcher,
+    TaggedUnionMatcherFactory,
+    TaggedUnionMatcherW,
+    TaggedUnionMatcherWFactory,
+} from "./tagged-union.ts";