feat/cover-pdf-builder

[NeurArk]

What

• add PdfReportBuilder with cover/summary support
• allow multiple styled charts
• document new fields and advanced usage
• provide demo PDF with new layout
• adjust tests for new builder API

Why

• generate professional multi‑page PDFs
• demonstrate new schema options

How

• refactor create_pdf around PdfReportBuilder
• extend pdf_schema.json with summary and chart options
• update unit tests to cover builder and new features

Test Plan

• ruff format --check .
• ruff check .
• pytest -q --cov=tools --cov=agent --cov-report=term-missing --cov-fail-under=85
• mypy tools/ agent/ tests/ --python-version 3.12
• bandit -r tools/ agent/ -ll -x /tests/

MCP Impact

• pdf tool now accepts summary and styled chart specs
• schema updated accordingly