Refactor chart renderer boundaries and dispatch¶

Problem¶

The chart rendering layer still mixes orchestration, Dataface JSON serialization, SVG-native export conversion, and Vega-Lite spec generation in a small number of entrypoints. This makes the renderer harder to reason about, harder to test in isolation, and prone to accidental regressions when changing one output path. Split render_chart() and generate_vega_lite_spec() into thinner orchestration methods with explicit helper modules for dispatch and output handling, while preserving behavior and existing snapshot and test coverage.

Refactor chart renderer boundaries and dispatch¶

Problem¶

Context¶

Possible Solutions¶

Plan¶

Implementation Progress¶

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