feat(quality): add L0 quality layer (Track A1 + A2 of dev plan)

L0 quality detection layer to catch translation failures BEFORE they
reach users. Pure Python/TypeScript, zero new dependencies, no API calls.

Backend (Python — services/quality/):
  - Script detection: 145 langs mapped to 23 scripts (Latin, Cyrillic,
    Greek, Arabic, Hebrew, CJK, Hangul, Kana, Devanagari, Bengali, etc.)
  - Language confusion detection (e.g. Arabic text for French target)
  - Arabic-script variant discrimination (Persian/Urdu/Pashto/Kurdish
    confusion — e.g. Persian text returned when Arabic was requested)
  - Length sanity check (with numeric/short-source exemptions)
  - Prompt leak detection (Translation: / Voici la traduction: / 翻译:)
  - Repetition hallucination detection (token + character level)
  - File text extraction for .docx/.xlsx/.pptx/.pdf (no translator
    changes needed)
  - Defensive pipeline that never raises (L0 must NEVER break a job)

Frontend (TypeScript — wordly.art---traduction-de-documents/src/utils/):
  - Exact 1:1 mirror of the Python module
  - Zero dependencies, works in browser AND Node.js
  - Native Unicode regex (\\p{L}/u) and codePoint iteration
  - 63 tests using Node's built-in test runner

Integration:
  - Feature-flagged: QUALITY_L0_ENABLED=false (default)
  - Observation only: logs structured events, never modifies files
  - try/except wrapped: impossible to break a translation job
  - Lazy imports: only loaded when flag is on
  - Zero impact on existing tests / behavior

Tests:
  - 111 Python tests covering all paths (config, script, length, leak,
    pipeline, file_extractor) — 100% pass
  - 63 TypeScript tests (Node --test) — 100% pass
  - 174/174 total tests for the L0 layer

Bug fixes in script mapping:
  - yi (Yiddish) -> hebrew (was incorrectly mapped to arabic)
  - dv (Maldivian) -> thaana (was incorrectly mapped to arabic)
  - ja (Japanese) -> hiragana_katakana (distinguishes from Chinese CJK)

Phase 1 (backend) + Phase 2 (frontend) of Track A complete.
Next: Track B1 (Word/Excel format preservation quick wins).

Closes Track A phase 1+2 of the dev plan.

services/quality/__init__.py

@@ -0,0 +1,35 @@
+"""
+Quality check layer for translations.
+
+Track A1 — L0 backend (observation only).
+Pure Python, no new dependencies, no network calls.
+Designed to be ADDITIVE: existing translation flow is untouched.
+
+Public API:
+    QualityCheckResult         — per-chunk result dataclass
+    DocumentQualityResult      — aggregated result dataclass
+    evaluate_chunk(...)        — score a single (source, translation) pair
+    evaluate_document(...)     — score a list of pairs and aggregate
+    run_l0_check(...)          — defensive wrapper used by the route
+    extract_sample(...)        — extract text from a finished file
+"""
+
+from .script_detector import (
+    QualityCheckResult,
+    DocumentQualityResult,
+    evaluate_chunk,
+    evaluate_document,
+    detect_arabic_variant,
+)
+from .pipeline import run_l0_check
+from .file_extractor import extract_sample
+
+__all__ = [
+    "QualityCheckResult",
+    "DocumentQualityResult",
+    "evaluate_chunk",
+    "evaluate_document",
+    "detect_arabic_variant",
+    "run_l0_check",
+    "extract_sample",
+]