feat: H1 to H2 setting with the admin save conversion (tracer)

- content_h1_to_h2 and generic_anchors on the settings row (migration
  202610280001), Headings and links tab, config key
  golem15.journal.content_h1_to_h2 used when no settings row exists
- classes.ConvertH1 on the x/net/html tokenizer; the Blog Editor types
  convert while the setting is on and answer editor.h1_converted
- GET /posts/{slug} reports content_h1_to_h2 (additive key)

classes/journal_settings.go

@@ -0,0 +1,84 @@
+package classes
+
+import (
+	"context"
+	"strings"
+
+	"git.golem15.com/golem15/sm-journal-plugin/models"
+	"git.golem15.com/golem15/summercms/modules/compass"
+	"gorm.io/gorm"
+)
+
+// H1ToH2Key is the config key of the H1 setting, used only when the Journal
+// settings row does not exist (EffectiveH1ToH2). Its shipped default is true.
+const H1ToH2Key = "golem15.journal.content_h1_to_h2"
+
+// DefaultGenericAnchors are the link texts the editor warns about when the
+// settings row has no list of its own: the English and the Polish seed list,
+// each entry once.
+var DefaultGenericAnchors = []string{
+	"click here", "here", "more", "read more", "learn more", "this link", "link",
+	"kliknij tutaj", "tutaj", "tu", "więcej", "czytaj więcej", "czytaj dalej", "ten link",
+}
+
+// headingSettings is the part of the settings row the heading rules read.
+type headingSettings struct {
+	ContentH1ToH2  bool
+	GenericAnchors *string
+}
+
+// readHeadingSettings reads the settings row (ID 1); found is false when
+// there is no row or no database.
+func readHeadingSettings(ctx context.Context, db *gorm.DB) (headingSettings, bool) {
+	if db == nil {
+		return headingSettings{}, false
+	}
+	if ctx != nil {
+		db = db.WithContext(ctx)
+	}
+	var rows []headingSettings
+	if err := db.Model(&models.Settings{}).Select("content_h1_to_h2", "generic_anchors").
+		Where("id = ?", 1).Limit(1).Find(&rows).Error; err != nil || len(rows) == 0 {
+		return headingSettings{}, false
+	}
+	return rows[0], true
+}
+
+// EffectiveH1ToH2 is the one reader of the H1 setting (P33-04): the settings
+// row's content_h1_to_h2 decides; without a row (or a database) the config
+// key golem15.journal.content_h1_to_h2 does, and true when that is unset
+// too. While it is true every H1 saved in Journal rich text becomes an H2.
+func EffectiveH1ToH2(ctx context.Context, db *gorm.DB, cfg *compass.Config) bool {
+	if row, ok := readHeadingSettings(ctx, db); ok {
+		return row.ContentH1ToH2
+	}
+	if cfg != nil && cfg.Has(H1ToH2Key) {
+		return cfg.Bool(H1ToH2Key)
+	}
+	return true
+}
+
+// GenericAnchors is the list of generic link texts: the settings row's
+// generic_anchors, one entry per line, trimmed and lowercased with blank
+// lines dropped, or DefaultGenericAnchors when the row has no list (no
+// row, NULL or only blank lines).
+func GenericAnchors(ctx context.Context, db *gorm.DB) []string {
+	row, ok := readHeadingSettings(ctx, db)
+	if !ok || row.GenericAnchors == nil {
+		return append([]string(nil), DefaultGenericAnchors...)
+	}
+	var out []string
+	seen := map[string]bool{}
+	for _, line := range strings.Split(*row.GenericAnchors, "\n") {
+		entry := strings.ToLower(strings.TrimSpace(line))
+		if entry == "" || seen[entry] {
+			continue
+		}
+		seen[entry] = true
+		out = append(out, entry)
+	}
+	if len(out) == 0 {
+		return append([]string(nil), DefaultGenericAnchors...)
+	}
+	return out
+}