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)

services/providers/config.py

@@ -96,38 +96,47 @@ class ProvidersConfig:
     DEEPSEEK_MAX_RETRIES: int = int(os.getenv("DEEPSEEK_MAX_RETRIES", "3"))
     DEEPSEEK_RETRY_DELAY: float = float(os.getenv("DEEPSEEK_RETRY_DELAY", "1.0"))
 
-    # Minimax (direct API - m2.7, MiniMax-M1)
+    # Minimax (public OpenAI-compatible API - https://api.minimax.io)
     MINIMAX_ENABLED: bool = os.getenv("MINIMAX_ENABLED", "false").lower() == "true"
     MINIMAX_API_KEY: str = os.getenv("MINIMAX_API_KEY", "")
-    MINIMAX_MODEL: str = os.getenv("MINIMAX_MODEL", "MiniMax-M1")
-    MINIMAX_BASE_URL: str = os.getenv("MINIMAX_BASE_URL", "https://api.minimax.chat/v1")
+    MINIMAX_MODEL: str = os.getenv("MINIMAX_MODEL", "MiniMax-M3")
+    MINIMAX_BASE_URL: str = os.getenv("MINIMAX_BASE_URL", "https://api.minimax.io/v1")
     MINIMAX_GROUP_ID: str = os.getenv("MINIMAX_GROUP_ID", "")
     MINIMAX_TIMEOUT: int = int(os.getenv("MINIMAX_TIMEOUT", "60"))
     MINIMAX_MAX_RETRIES: int = int(os.getenv("MINIMAX_MAX_RETRIES", "3"))
     MINIMAX_RETRY_DELAY: float = float(os.getenv("MINIMAX_RETRY_DELAY", "1.0"))
 
     # Fallback chain configuration
-    # General fallback chain (backward compatibility)
+    #
+    # IMPORTANT: the registry-based fallback (translate_with_fallback) only
+    # ever sees providers that _auto_register_providers() registers, i.e.
+    # google, deepl, openai, deepseek and minimax. The OpenAI-compatible
+    # shims (openrouter, openrouter_premium, zai) and google_cloud are wired
+    # directly in routes/translate_routes.py and are intentionally NOT part of
+    # the registry fallback chain — listing them here would make
+    # translate_with_fallback silently skip them with a "provider not
+    # registered" log on every call. Override via env if you know what you
+    # are doing.
     FALLBACK_CHAIN: List[str] = [
         name.strip()
         for name in os.getenv(
-            "PROVIDER_FALLBACK_CHAIN", "google,google_cloud,deepl,openrouter,openrouter_premium,openai,deepseek,zai"
+            "PROVIDER_FALLBACK_CHAIN", "google,deepl,openai,deepseek,minimax"
         ).split(",")
         if name.strip()
     ]
 
     # Mode-specific fallback chains
-    # Classic mode: Google Translate -> Google Cloud -> DeepL
+    # Classic mode: Google Translate -> DeepL
     FALLBACK_CHAIN_CLASSIC: List[str] = [
         name.strip()
-        for name in os.getenv("FALLBACK_CHAIN_CLASSIC", "google,google_cloud,deepl").split(",")
+        for name in os.getenv("FALLBACK_CHAIN_CLASSIC", "google,deepl").split(",")
         if name.strip()
     ]
 
-    # LLM mode: cloud providers in order of cost/quality (no Ollama by default)
+    # LLM mode: cloud providers in order of cost/quality (registry-registered only)
     FALLBACK_CHAIN_LLM: List[str] = [
         name.strip()
-        for name in os.getenv("FALLBACK_CHAIN_LLM", "openrouter,openrouter_premium,openai,deepseek,zai").split(",")
+        for name in os.getenv("FALLBACK_CHAIN_LLM", "openai,deepseek,minimax").split(",")
         if name.strip()
     ]