feat(translation): quality pipeline overhaul + new features (audit 2026-08-29)

Translation quality & format preservation:
- Word: merge adjacent same-format runs into one unit (sentence-level
  coherence like inline-tag handling); translate comments/balloons;
  dedupe textbox collection (was translated twice); RTL no longer
  overrides center/justify alignment; CJK/Arabic font hints (eastAsia/cs)
- PPTX: chart translations now actually reach the output file
  (ChartPart.blob is read-only — rewrite chart XML in the saved ZIP);
  CJK typeface hints (a:ea)
- Excel: sheet renames no longer break references — rewrite cell
  formulas (3D/quoted), defined names, data validations, cond. formats
- PDF: bold/italic honored (hebo/heit/hebi); table cells never merge;
  unchanged blocks left untouched (typography preserved, fixes duplicate
  hyperlinks); attempted/changed stats + route gate now cover PDF;
  CJK font paths; scanned PDFs via Mistral OCR (detection + admin settings)

Features:
- formality param (formal/informal) + automatic regional-variant prompts
- output_mode=bilingual docx (source above translation)
- per-user translation memory on Redis (falls back to LRU), context-hashed
- QA report + 0-100 confidence score in job status; L0 on by default
- OpenAI-compatible providers: whole chunk in ONE numbered-JSON request
  (~15x fewer calls) with per-item fallback; base prompt always present
  (custom prompt no longer replaces translation instructions)

Infra & marketing alignment:
- plan-based engine gating + vision gating (closes paid-engine leak);
  /providers/available filtered per plan; 107 languages exposed
- zh-CN/zh-TW validation fixed; libmagic disabled on Windows (native crash)
- admin: Mistral OCR settings + engine status dashboard; httpx<0.28 pin
  (TestClient breakage); Prometheus test fixture fixed
- marketing docs aligned with code (PDF+OCR, retention, engines, pricing)
- security: .env.ionos/.env.production/provider_settings.json removed

Tests: 1173 passed / 0 failed (6 network tests deselected: free Google
endpoint temporarily blocked from this machine)

tests/test_story_2_13_validation.py

@@ -30,10 +30,18 @@ def test_validate_invalid_magic_bytes():
     assert response.json()["error"] == "CORRUPTED_FILE"
     assert "corrompu" in response.json()["message"]
     
+def _minimal_zip() -> bytes:
+    """A real minimal ZIP archive (Office files are ZIPs)."""
+    import io, zipfile
+    buf = io.BytesIO()
+    with zipfile.ZipFile(buf, "w") as zf:
+        zf.writestr("[Content_Types].xml", "<Types/>")
+    return buf.getvalue()
+
+
 def test_validate_valid_file_header():
-    # Test with a minimal valid-looking zip (Office files are ZIPs)
-    # FileValidator checks for b"PK\x03\x04"
-    files = {"file": ("test.docx", b"PK\x03\x04" + b"\x00" * 20, "application/vnd.openxmlformats-officedocument.wordprocessingml.document")}
+    # Minimal real ZIP: passes magic-byte AND zip-safety checks
+    files = {"file": ("test.docx", _minimal_zip(), "application/vnd.openxmlformats-officedocument.wordprocessingml.document")}
     response = client.post(
         "/api/v1/translate",
         files=files,