Store category prompts as EXACT split legacy text, no boilerplate

The per-category prompt editor showed English machine boilerplate
("Role: description. Build JSON …", schema intro, {{var}} context lines)
because seed/sync baked the render framing into categories.prompt. Now the
stored overlay is exactly the legacy wp_product_categories.sql content,
split into the three sections a user would type themselves:

  --- Title ---        Slovenian naming formula
  --- Description ---  legacy <H2>/<p>/<ul> body structure
  --- Meta ---         legacy metaDescription instruction

Schema, role framing, and Name/Description/Category/Attrs product context
stay render-time only (system template + ensureCategoryEnhanceUserContext),
where they already existed.

- SplitLegacyCombinedEnhancePrompt: non-legacy input now returns "" —
  categories without seed/legacy content get their override CLEARED
  (company default) instead of being stuffed with the canonical template
  (e.g. parent categories like "Bela tehnika" absent from the SQL).
- CategoryEnhancePromptNeedsRepair flags stored boilerplate ("parsed as
  JSON", "Build JSON", retired Attributes section) so Sync rewrites old
  data to the clean shape; repair supports clearing (prompt = '{}').
- seed-a1 apply-category-prompts skips instead of writing template text.
- Web editor compose stores only the user's section text: empty sections
  keep bare markers, default bodies and the default preamble are never
  persisted (DEFAULT_SECTION_BODIES removed).
- Verified locally: apply rewrote 238 A1+Demo categories (216 exact
  splits, 22 cleared), zero boilerplate matches in DB, idempotent re-run
  (would_update=0).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/api/internal/aiprompts/title_formula_test.go

@@ -86,12 +86,17 @@ func TestTitleRoleInstructionNeverBrandOnly(t *testing.T) {
 	if !strings.Contains(CategoryEnhanceUserTemplate, TitleRoleInstruction) {
 		t.Fatal("CategoryEnhanceUserTemplate must embed TitleRoleInstruction")
 	}
+	// Split overlays carry ONLY the legacy per-category text; the never-brand-only
+	// rule lives in the render-time role framing, not the stored prompt.
 	split := SplitLegacyCombinedEnhancePrompt(`GPT predloga:
 <name>{Napiši tip izdelka, znamka, poln model}</name>
 <metaDescription>{140 znakov}</metaDescription>
 <H2>{benefit}</H2>`)
-	if !strings.Contains(split, "never brand-only") {
-		t.Fatalf("split Title section missing never brand-only: %s", split)
+	if strings.Contains(split, "never brand-only") {
+		t.Fatalf("split overlay must not embed role boilerplate: %s", split)
+	}
+	if !strings.Contains(split, "Napiši tip izdelka, znamka, poln model") {
+		t.Fatalf("split Title section must keep the legacy naming text: %s", split)
 	}
 }