feat: Notifiers CRUD (#337)

* introduce scaffold for new models

* wip: shoutrrr wrapper (may remove)

* update schema files

* gen: ent code

* gen: migrations

* go mod tidy

* add group_id to notifier

* db migration

* new mapper helpers

* notifier repo

* introduce experimental adapter pattern for hdlrs

* refactor adapters to fit more common use cases

* new routes for notifiers

* update errors to fix validation panic

* go tidy

* reverse checkbox label display

* wip: notifiers UI

* use badges instead of text

* improve documentation

* add scaffold schema reference

* remove notifier service

* refactor schema folder

* support group edges via scaffold

* delete test file

* include link to API docs

* audit and update documentation + improve format

* refactor schema edges

* refactor

* add custom validator

* set validate + order fields by name

* fix failing tests

backend/internal/data/repo/automappers.go

@@ -0,0 +1,32 @@
+package repo
+
+type MapFunc[T any, U any] func(T) U
+
+func (a MapFunc[T, U]) Map(v T) U {
+	return a(v)
+}
+
+func (a MapFunc[T, U]) MapEach(v []T) []U {
+	result := make([]U, len(v))
+	for i, item := range v {
+		result[i] = a(item)
+	}
+	return result
+}
+
+func (a MapFunc[T, U]) MapErr(v T, err error) (U, error) {
+	if err != nil {
+		var zero U
+		return zero, err
+	}
+
+	return a(v), nil
+}
+
+func (a MapFunc[T, U]) MapEachErr(v []T, err error) ([]U, error) {
+	if err != nil {
+		return nil, err
+	}
+
+	return a.MapEach(v), nil
+}