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)

models/settings.go

@@ -17,6 +17,12 @@ type Settings struct {
 	RSSCopyright        *string `gorm:"column:rss_copyright"`
 	RSSImageURL         *string `gorm:"column:rss_image_url"`
 	RSSPostsPerFeed     int     `gorm:"column:rss_posts_per_feed"`
+	// ContentH1ToH2 turns H1 in Journal rich text (post content and
+	// category pillar text) into H2 on every write path.
+	ContentH1ToH2 bool `gorm:"column:content_h1_to_h2"`
+	// GenericAnchors lists the link texts the editor warns about, one per
+	// line; nil means the built-in lists.
+	GenericAnchors *string `gorm:"column:generic_anchors"`
 }
 
 func (Settings) TableName() string { return "golem15_journal_settings" }
@@ -27,6 +33,7 @@ func (Settings) Fillable() []string {
 		"search_title_weight", "search_excerpt_weight", "search_content_weight",
 		"rss_enabled", "rss_include_content", "rss_title", "rss_description",
 		"rss_language", "rss_copyright", "rss_image_url", "rss_posts_per_feed",
+		"content_h1_to_h2", "generic_anchors",
 	}
 }
 
@@ -46,6 +53,8 @@ func (Settings) Rules() map[string]string {
 		"rss_copyright":         "nullable|string|max:255",
 		"rss_image_url":         "nullable|url|max:500",
 		"rss_posts_per_feed":    "nullable|integer|min:1|max:100",
+		"content_h1_to_h2":      "boolean",
+		"generic_anchors":       "nullable|string|max:5000",
 	}
 }