feat: journal:fix-headings and the settings API

- classes.FixStoredHeadings converts stored H1 in post content (every
  locale) and category pillar text, in one transaction with a RecordSaved
  and a site cache purge per changed record
- journal:fix-headings, a dry run unless --apply, refuses with exit code 1
  while the H1 setting is off
- GET/PUT /_journal/api/v1/settings and POST /fix-headings {dry_run} for
  golem15.journal.manage_settings; 409 with the refusal while the setting
  is off

controllers/api/maintenance.go

@@ -0,0 +1,53 @@
+package api
+
+import (
+	"net/http"
+
+	"git.golem15.com/golem15/sm-journal-plugin/classes"
+	"git.golem15.com/golem15/summercms/modules/backpack"
+	"git.golem15.com/golem15/summercms/modules/wire"
+)
+
+// FixHeadings is POST /_journal/api/v1/fix-headings {dry_run}: the
+// journal:fix-headings conversion of stored H1 headings (posts in every
+// locale and category pillar text), for golem15.journal.manage_settings. It
+// is a dry run unless dry_run is false, and answers {posts, categories,
+// headings, dry_run}. While the H1 setting is off it refuses with 409 and
+// the refusal phrase. MCP journal_fix_headings.
+func FixHeadings(app *backpack.App) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		r, pr, ok := requireBackendPrincipal(app, w, r)
+		if !ok || !requireManageSettings(w, pr) {
+			return
+		}
+		db, err := gdb(app)
+		if err != nil {
+			writeAPIError(w, http.StatusInternalServerError, "Internal server error")
+			return
+		}
+		body, err := readJSONObject(r)
+		if err != nil {
+			writeAPIError(w, http.StatusBadRequest, errValidationFailed)
+			return
+		}
+		dry := true
+		if v, has := body["dry_run"]; has && v != nil {
+			dry = asBool(v)
+		}
+		if !classes.EffectiveH1ToH2(r.Context(), db, appConfig(app)) {
+			writeAPIError(w, http.StatusConflict, classes.H1ConversionOffText)
+			return
+		}
+		res, err := classes.FixStoredHeadings(r.Context(), app, db, !dry)
+		if err != nil {
+			writeAPIError(w, http.StatusInternalServerError, "Internal server error")
+			return
+		}
+		wire.WriteJSON(w, http.StatusOK, map[string]any{
+			"posts":      res.Posts,
+			"categories": res.Categories,
+			"headings":   res.Headings,
+			"dry_run":    dry,
+		})
+	}
+}