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/robots_write.go

@@ -0,0 +1,111 @@
+package classes
+
+import (
+	"context"
+	"errors"
+	"strconv"
+	"time"
+
+	"git.golem15.com/golem15/sm-seo-plugin/models"
+	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
+)
+
+// RobotsRow returns robots row 1 inside db, creating it when the
+// migration's row is gone (first or create, safe against a concurrent
+// first request).
+func RobotsRow(db *gorm.DB) (models.Robots, error) {
+	var rows []models.Robots
+	if err := db.Where("id = ?", 1).Limit(1).Find(&rows).Error; err != nil {
+		return models.Robots{}, err
+	}
+	if len(rows) > 0 {
+		return rows[0], nil
+	}
+	row := models.Robots{ID: 1, Bots: models.BotSwitches{}}
+	if err := db.Clauses(clause.OnConflict{DoNothing: true}).Create(&row).Error; err != nil {
+		return models.Robots{}, err
+	}
+	if err := db.Where("id = ?", 1).Limit(1).Find(&rows).Error; err != nil {
+		return models.Robots{}, err
+	}
+	if len(rows) == 0 {
+		return models.Robots{}, errors.New("golem15.seo: robots row is missing")
+	}
+	return rows[0], nil
+}
+
+// RobotsValues are the robots row's values for history: the editor's text
+// and every listed bot's switch.
+func RobotsValues(r models.Robots) map[string]any {
+	bots := map[string]any{}
+	for _, b := range Bots {
+		bots[b.Token] = r.Bots.Allowed(b.Token)
+	}
+	return map[string]any{"content": r.Content, "bots": bots}
+}
+
+// RobotsWrite is one change of robots.txt: the editor's text when Content
+// is set, and the switches of the bots listed in Bots (by token).
+type RobotsWrite struct {
+	Content *string
+	Bots    map[string]bool
+}
+
+// SaveRobots writes robots.txt inside tx and records it in history
+// (D-22, D-25). A text over MaxRobotsBytes and a token that is not a
+// listed AI bot are refused with a *ProblemsError. It returns the stored
+// row and the noindex addresses Googlebot may no longer fetch under it
+// (the robots.blocks_noindex warning).
+func (s *Service) SaveRobots(ctx context.Context, tx *gorm.DB, in RobotsWrite) (models.Robots, []string, error) {
+	row, err := RobotsRow(tx)
+	if err != nil {
+		return models.Robots{}, nil, err
+	}
+	problems := map[string][]models.Problem{}
+	if in.Content != nil && len(*in.Content) > MaxRobotsBytes {
+		problems["content"] = append(problems["content"], models.Problem{Key: "golem15.seo::lang.robots.too_large"})
+	}
+	for token := range in.Bots {
+		if _, ok := BotByToken(token); !ok {
+			problems["bots."+token] = append(problems["bots."+token], models.Problem{Key: "golem15.seo::lang.api.bot_unknown"})
+		}
+	}
+	if len(problems) > 0 {
+		return models.Robots{}, nil, &ProblemsError{Problems: problems}
+	}
+	before := RobotsValues(row)
+	if in.Content != nil {
+		row.Content = *in.Content
+	}
+	bots := models.BotSwitches{}
+	for token, on := range row.Bots {
+		bots[token] = on
+	}
+	for token, on := range in.Bots {
+		b, _ := BotByToken(token)
+		bots[b.Token] = on
+	}
+	row.Bots = bots
+	now := time.Now().UTC()
+	row.UpdatedAt = &now
+	if err := tx.Model(&models.Robots{}).Where("id = ?", row.ID).Updates(map[string]any{
+		"content": row.Content, "bots": row.Bots, "updated_at": now,
+	}).Error; err != nil {
+		return models.Robots{}, nil, err
+	}
+	if err := s.Record(ctx, tx, Change{
+		Kind:      models.SubjectRobots,
+		SubjectID: strconv.FormatUint(uint64(row.ID), 10),
+		What:      s.Phrase("golem15.seo::lang.history.what_robots", nil),
+		Before:    before,
+		After:     RobotsValues(row),
+	}); err != nil {
+		return models.Robots{}, nil, err
+	}
+	blocked, err := s.BlockedNoindex(tx, row.Content, row.Bots)
+	if err != nil {
+		return models.Robots{}, nil, err
+	}
+	return row, blocked, nil
+}