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

Porta da main la riscrittura completa di conversione/_pipeline/ (9 stadi
PyMuPDF) e la suite tests/ senza modificare chunks/, step-8/, rag.py,
ollama/, 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>

tests/unit/test_models.py

@@ -0,0 +1,47 @@
+"""Test dataclass Block, Section, FontProfile."""
+from conversione._pipeline.models import Block, Section, FontProfile
+
+
+def test_block_creation():
+    b = Block(
+        text="Titolo", page=1,
+        bbox=(0, 0, 100, 14),
+        font_size=16.0, font_name="Arial-Bold",
+        is_bold=True,
+    )
+    assert b.text == "Titolo"
+    assert b.is_bold
+    assert b.block_type == "paragraph"
+    assert b.level == 0
+    assert b.x0 == 0.0
+    assert b.y1 == 14.0
+
+
+def test_block_properties():
+    b = Block("x", 1, (10.0, 20.0, 110.0, 34.0), 12.0, "Helvetica", False)
+    assert b.x0 == 10.0
+    assert b.y0 == 20.0
+    assert b.x1 == 110.0
+    assert b.y1 == 34.0
+
+
+def test_section_defaults():
+    s = Section(title="Intro", level=1)
+    assert s.content == []
+    assert s.children == []
+    assert s.page_start == 0
+
+
+def test_section_nesting():
+    parent = Section("Parent", level=1)
+    child  = Section("Child", level=2)
+    parent.children.append(child)
+    assert len(parent.children) == 1
+    assert parent.children[0].title == "Child"
+
+
+def test_font_profile():
+    fp = FontProfile(body_size=11.0, cluster_map={18.0: 1, 15.0: 2}, header_sizes=[18.0, 15.0])
+    assert fp.body_size == 11.0
+    assert fp.cluster_map[18.0] == 1
+    assert len(fp.header_sizes) == 2