feat: integra pipeline PDF→Markdown a 9 stadi e test suite

Porta da branch marker la riscrittura completa di conversione/_pipeline/
(9 stadi PyMuPDF) e la suite tests/ senza modificare il resto del progetto
RAG (ollama/, step-5/, step-6/, step-8/, rag.py, retrieve.py, config.py).

requirements.txt: aggiunge PyMuPDF>=1.24.0 e pytest>=8.0, mantiene chromadb,
rimuove opendataloader-pdf e pymupdf4llm.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

conversione/_pipeline/_helpers.py

@@ -0,0 +1,153 @@
+"""Funzioni helper pure condivise tra i moduli di trasformazione."""
+import re
+
+from ._constants import _ORDINALS_IT, _ORDINALS_EN
+
+
+def _sentence_case(s: str) -> str:
+    if not s:
+        return s
+    lower = s.lower()
+    return lower[0].upper() + lower[1:]
+
+
+def _is_allcaps_line(line: str) -> bool:
+    stripped = line.strip()
+    letters  = [c for c in stripped if c.isalpha()]
+    return (
+        len(letters) >= 3
+        and all(c.isupper() for c in letters)
+        and not stripped.startswith("#")
+        and not stripped.startswith("|")
+    )
+
+
+def _allcaps_to_header(raw_line: str) -> str:
+    text = re.sub(r"^[-*+]\s+", "", raw_line.strip())
+    text = text.rstrip(".").rstrip("?").strip()
+
+    _ORD_IT_PAT = "|".join(_ORDINALS_IT.keys())
+    m = re.match(rf"^CAPITOLO ({_ORD_IT_PAT})\. (.+)", text)
+    if m:
+        roman  = _ORDINALS_IT[m.group(1)]
+        titolo = m.group(2).rstrip(".").rstrip("?").strip()
+        return f"## Capitolo {roman} — {_sentence_case(titolo)}"
+
+    _ORD_EN_PAT = "|".join(_ORDINALS_EN.keys())
+    m = re.match(rf"^CHAPTER ({_ORD_EN_PAT}|\d+)\.? (.+)", text)
+    if m:
+        n      = _ORDINALS_EN.get(m.group(1), m.group(1))
+        titolo = m.group(2).rstrip(".").rstrip("?").strip()
+        return f"## Chapter {n} — {_sentence_case(titolo)}"
+
+    m = re.match(r"^([IVXLCDM]+|[0-9]+)\. (.+)", text)
+    if m:
+        return f"## {m.group(1)}. {_sentence_case(m.group(2).rstrip('.').strip())}"
+
+    return f"## {_sentence_case(text)}"
+
+
+def _extract_math_environments(text: str) -> tuple[str, int]:
+    _ENVS = (
+        r"Definizione|Definition|Teorema|Theorem|Lemma|"
+        r"Proposizione|Proposition|Corollario|Corollary|"
+        r"Osservazione|Remark|Nota|Note|Esempio|Example"
+    )
+    count  = 0
+    blocks = text.split("\n\n")
+    result = []
+
+    for block in blocks:
+        stripped = block.strip()
+        if not stripped or stripped.startswith("#"):
+            result.append(block)
+            continue
+
+        m = re.match(
+            rf"^({_ENVS})\s+((?:\d+\.?){{1,4}})\s*(.*)",
+            stripped,
+            re.DOTALL,
+        )
+        if not m:
+            result.append(block)
+            continue
+
+        env  = m.group(1)
+        num  = m.group(2).rstrip(".")
+        rest = m.group(3).strip()
+
+        title_m = re.match(r"^(\([^)]{2,60}\))\s+(.*)", rest, re.DOTALL)
+        if title_m:
+            header = f"### {env} {num} {title_m.group(1)}"
+            body   = title_m.group(2).strip()
+        else:
+            header = f"### {env} {num}."
+            body   = rest
+
+        result.append(f"{header}\n\n{body}" if body else header)
+        count += 1
+
+    return "\n\n".join(result), count
+
+
+def _merge_title_headers(text: str) -> tuple[str, int]:
+    count  = 0
+    blocks = re.split(r"\n{2,}", text)
+    result = []
+    i = 0
+    while i < len(blocks):
+        block    = blocks[i]
+        stripped = block.strip()
+        if (
+            re.match(r"^#{2,3} \d+\.\s*$", stripped)
+            and i + 1 < len(blocks)
+        ):
+            nxt = blocks[i + 1].strip()
+            if (
+                nxt
+                and "\n" not in nxt
+                and len(nxt) <= 80
+                and not nxt.startswith("#")
+                and not re.match(r"^\d+[\.\)]\s", nxt)
+            ):
+                result.append(stripped.rstrip() + " " + nxt)
+                count += 1
+                i += 2
+                continue
+        result.append(block)
+        i += 1
+    return re.sub(r"\n{3,}", "\n\n", "\n\n".join(result)), count
+
+
+def _extract_article_headers(text: str) -> tuple[str, int]:
+    count = 0
+
+    def _repl(m: re.Match) -> str:
+        nonlocal count
+        num  = m.group(1)
+        rest = m.group(2).strip()
+
+        title_m = re.match(
+            r"^([A-Z\xc0\xc8\xc9\xcc\xcd\xd2\xd3\xd9\xda].{1,74}?)\.\s+"
+            r"([A-Z\xc0\xc8\xc9\xcc\xcd\xd2\xd3\xd9\xda\(\d].{4,})",
+            rest,
+        )
+        if title_m:
+            count += 1
+            return (
+                f"### Art. {num}. {title_m.group(1)}.\n\n"
+                f"{title_m.group(2).strip()}"
+            )
+        if rest:
+            count += 1
+            return f"### Art. {num}.\n\n{rest}"
+        count += 1
+        return f"### Art. {num}."
+
+    text = re.sub(
+        r"^-\s+Art\.\s+([\d]+[a-z\-]*)\.\s*(.*)",
+        _repl,
+        text,
+        flags=re.MULTILINE,
+    )
+    return text, count