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/roles_test.go

@@ -25,8 +25,10 @@ func TestCategoryEnhanceHasRoleSections(t *testing.T) {
 	if !CategoryEnhancePromptNeedsRepair(old) {
 		t.Fatal("old attributes-bearing prompt must need repair (attributes section retired)")
 	}
-	if CategoryEnhancePromptNeedsRepair(CategoryEnhanceUserTemplate) {
-		t.Fatal("canonical template must not need repair")
+	// The built-in template is render-time only; a STORED copy is boilerplate
+	// pollution and must be repaired (cleared to company default).
+	if !CategoryEnhancePromptNeedsRepair(CategoryEnhanceUserTemplate) {
+		t.Fatal("stored canonical template text must need repair")
 	}
 }