Implement native DrawingML chart rendering

[davidnmbond]

Deferred from phase 9 step 9.1.1.

Scope:

• Render common embedded Word charts natively from chart parts
• Support at least bar, line, and pie charts
• Produce SVG and PDF output without relying on cached fallback images when possible

Acceptance criteria:

• Common chart types render natively from DrawingML chart parts
• SVG and PDF outputs are covered by tests
• Document known unsupported chart types and fidelity limits