feat: management API and an MCP tool per SEO admin operation

- /_seo/api/v1 routes for the effective SEO of a URL with sources and
  owner, URL rules, redirects (loops refused with redirect_loop), the
  404 log actions, robots.txt and its tester, settings and history
- the CMS-data issue report: missing and duplicate titles and
  descriptions, rules over records, redirect chains, canonicals to
  noindex or redirected addresses, noindex addresses robots.txt blocks
- 24 MCP tools on those routes (backend guard, golem15.seo.manage)
- AdminOperations maps every admin operation to its tool;
  TestEveryAdminOperationHasTool and TestMCPReadToolsAreGET guard drift
- robots.txt writes go through classes.SaveRobots from the admin too

classes/manage.go

@@ -0,0 +1,64 @@
+package classes
+
+import (
+	"context"
+	"strconv"
+
+	"git.golem15.com/golem15/sm-seo-plugin/models"
+	"gorm.io/gorm"
+)
+
+// LoadRedirect returns redirect id; ErrNoRecord when there is none.
+func LoadRedirect(db *gorm.DB, id uint) (models.Redirect, error) {
+	var rows []models.Redirect
+	if err := db.Where("id = ?", id).Limit(1).Find(&rows).Error; err != nil {
+		return models.Redirect{}, err
+	}
+	if len(rows) == 0 {
+		return models.Redirect{}, ErrNoRecord
+	}
+	return rows[0], nil
+}
+
+// LoadNotFound returns 404 log entry id; ErrNoRecord when there is none.
+func LoadNotFound(db *gorm.DB, id uint) (models.NotFound, error) {
+	var rows []models.NotFound
+	if err := db.Where("id = ?", id).Limit(1).Find(&rows).Error; err != nil {
+		return models.NotFound{}, err
+	}
+	if len(rows) == 0 {
+		return models.NotFound{}, ErrNoRecord
+	}
+	return rows[0], nil
+}
+
+// NotFoundValues are a 404 log entry's values for history.
+func NotFoundValues(n models.NotFound) map[string]any {
+	return map[string]any{"url": n.URL, "hits": n.Hits, "referer": n.Referer}
+}
+
+// DeleteNotFound removes a 404 log entry inside tx and records it in
+// history; the address is logged again on its next 404.
+func (s *Service) DeleteNotFound(ctx context.Context, tx *gorm.DB, n models.NotFound) error {
+	if err := tx.Delete(&models.NotFound{}, n.ID).Error; err != nil {
+		return err
+	}
+	return s.Record(ctx, tx, Change{
+		Kind:      models.SubjectNotFound,
+		SubjectID: strconv.FormatUint(uint64(n.ID), 10),
+		What:      s.Phrase("golem15.seo::lang.history.what_notfound", map[string]string{"url": n.URL}),
+		Before:    NotFoundValues(n),
+	})
+}
+
+// RedirectOrigin is the origin of a redirect created through ctx: mcp
+// through MCP, import through an import, else manual.
+func RedirectOrigin(ctx context.Context) string {
+	switch ViaOf(ctx) {
+	case models.ViaMCP:
+		return models.OriginMCP
+	case models.ViaImport:
+		return models.OriginImport
+	}
+	return models.OriginManual
+}