docs: templates de frontmatter YAML para function, pipeline, component y type

Añade plantillas de referencia que documentan el formato exacto
del frontmatter YAML que cada .md debe seguir. Cubren los cuatro
kinds: function, pipeline, component y type.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/templates/function.md

@@ -0,0 +1,32 @@
+---
+name: filter_slice
+kind: function
+lang: go
+domain: core
+version: "1.0.0"
+purity: pure
+signature: "func FilterSlice[T any](xs []T, pred func(T) bool) []T"
+description: "Filtra un slice aplicando un predicado sin mutar el original."
+tags: [slice, functional, generic]
+uses_functions: []
+uses_types: []
+returns: []
+returns_optional: false
+error_type: ""
+imports: []
+tested: false
+tests: []
+test_file_path: ""
+file_path: "functions/core/filter_slice.go"
+---
+
+## Ejemplo
+
+```go
+evens := FilterSlice([]int{1, 2, 3, 4}, func(n int) bool { return n%2 == 0 })
+// evens = [2, 4]
+```
+
+## Notas
+
+Funcion pura generica. No muta el slice original — crea uno nuevo.