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.

tests/services/quality/test_pipeline.py

@@ -0,0 +1,61 @@
+"""
+Tests for services/quality/pipeline.py
+"""
+import pytest
+
+from services.quality import run_l0_check
+from services.quality.script_detector import DocumentQualityResult
+
+
+class TestRunL0Check:
+    def test_returns_result_on_success(self):
+        result = run_l0_check(
+            ["Hello", "World"],
+            ["Bonjour", "Monde"],
+            "fr",
+            job_id="test_job_1",
+        )
+        assert isinstance(result, DocumentQualityResult)
+        assert result.passed is True
+        assert result.chunk_count == 2
+
+    def test_returns_neutral_on_empty_lists(self):
+        result = run_l0_check([], [], "fr", job_id="test_job_2")
+        assert result.passed is True
+        assert result.chunk_count == 0
+
+    def test_detects_failures(self):
+        result = run_l0_check(
+            ["Hello", "World"],
+            ["Bonjour", "مرحبا"],
+            "fr",
+            job_id="test_job_3",
+        )
+        assert result.passed is False
+        assert "wrong_script" in result.issues
+
+    def test_never_raises_on_bad_input(self):
+        # Even with weird input, it shouldn't raise
+        result = run_l0_check(
+            ["Hello"],
+            [None],  # None translation
+            "fr",
+            job_id="test_job_4",
+        )
+        assert result is not None
+
+    def test_optional_job_id(self):
+        # job_id is optional
+        result = run_l0_check(["hi"], ["salut"], "fr")
+        assert result is not None
+
+    def test_optional_file_extension(self):
+        result = run_l0_check(
+            ["hi"], ["salut"], "fr", file_extension=".docx"
+        )
+        assert result is not None
+
+    def test_target_lang_none(self):
+        # Should not crash with no target lang
+        result = run_l0_check(["hi"], ["salut"], None)
+        assert result is not None