feat: issue/0020 — generacion de PDFs en Python y Go

Añade 3 tipos Python (PDFDoc, PDFPage, PDFStyle) y 10 funciones Python
para construir PDFs con fpdf2 (builder fluent), fusionar PDFs con pypdf
y convertir HTML/Markdown a PDF via weasyprint (stub si no disponible).
Añade pdf_simple_report en Go como stub hasta que go-pdf/fpdf se integre.

- python/types/infra/: pdf_doc, pdf_page, pdf_style
- python/functions/infra/: pdf_create, pdf_add_page, pdf_add_text,
  pdf_add_table, pdf_add_image, pdf_add_header_footer, pdf_from_html,
  pdf_from_markdown, pdf_merge, pdf_save
- functions/infra/pdf_simple_report.go: stub Go con ReportSection/ReportTable
- 17 tests Python pasando (pytest)
- fpdf2 y pypdf añadidos via uv al venv Python

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

python/functions/infra/pdf_save_test.py

@@ -0,0 +1,43 @@
+"""Tests para pdf_save."""
+
+import sys
+import os
+import tempfile
+
+sys.path.insert(0, os.path.dirname(__file__))
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "..", "python", "types", "infra"))
+
+from pdf_create import pdf_create
+from pdf_add_page import pdf_add_page
+from pdf_add_text import pdf_add_text
+from pdf_save import pdf_save
+
+
+def _make_simple_doc():
+    doc = pdf_create(title="Test Save")
+    doc = pdf_add_page(doc)
+    doc = pdf_add_text(doc, "Contenido de prueba")
+    return doc
+
+
+def test_guardar_pdf_a_archivo():
+    doc = _make_simple_doc()
+    with tempfile.TemporaryDirectory() as tmpdir:
+        path = os.path.join(tmpdir, "test.pdf")
+        result = pdf_save(doc, path)
+        assert result == path
+        assert os.path.exists(path)
+        assert os.path.getsize(path) > 0
+
+
+def test_retornar_bytes_del_pdf():
+    doc = _make_simple_doc()
+    result = pdf_save(doc)
+    assert isinstance(result, bytes)
+    assert len(result) > 0
+
+
+def test_pdf_valido_comienza_con_pdf():
+    doc = _make_simple_doc()
+    pdf_bytes = pdf_save(doc)
+    assert pdf_bytes[:4] == b"%PDF"