fix(rtl): les textes centrs en persan s'affichaient du mauvais cote

- Word: sous w:bidi, w:jc est logique (left=dbut=droite visuelle,
  right=fin=gauche visuelle) ; forcer jc=right alignait donc les
  paragraphes a gauche et crasait le centrage hrit du style.
  Dsormais le RTL pose w:bidi et w:rtl sans jamais toucher w:jc,
  comme le fait Word lui-mme pour un document RTL.
- PowerPoint: algn n'est plus crit quand le paragraphe n'en dfinit
  pas, afin de respecter l'alignement hrit du masque (titres centrs) ;
  algn=l explicite reste converti en r (algn est visuel en DrawingML).
- tests: centrage par style Word prserv, aucun w:jic crit, algn
  absent non cras côté PowerPoint

translators/pptx_translator.py

@@ -73,9 +73,15 @@ def _set_pptx_paragraph_rtl(paragraph) -> None:
     Enable RTL mode on a PowerPoint paragraph.
 
     Sets rtl="1" on the <a:pPr> element, which controls the paragraph
-    text direction. The horizontal alignment (algn) is only forced to
-    "r" when the paragraph has no explicit alignment or is aligned
-    "l" (left) — a centered or justified title keeps its alignment.
+    text direction; with rtl="1" and no explicit algn, PowerPoint
+    renders the paragraph from its start edge — the right edge.
+
+    algn is only rewritten when the paragraph explicitly says "l": in
+    DrawingML algn is visual (not logical like Word's w:jc), so an
+    explicit left would keep RTL text on the left edge. When algn is
+    absent, the inherited layout/master alignment (often centered
+    titles) must keep playing — writing "r" here would override it,
+    which is the centered-text mis-rendering reported for Persian.
     """
     p_elem = paragraph._p
     tag_pPr = f"{{{_NS_A}}}pPr"
@@ -84,7 +90,7 @@ def _set_pptx_paragraph_rtl(paragraph) -> None:
         pPr = etree.Element(tag_pPr)
         p_elem.insert(0, pPr)
     pPr.set("rtl", "1")
-    if pPr.get("algn") in (None, "", "l"):
+    if pPr.get("algn") == "l":
         pPr.set("algn", "r")