uzor-render-svg — SVG serialization backend for uzor.

Implements [uzor::render::RenderContext] via [SvgRenderContext], but instead of rasterizing draw calls into a pixmap, it SERIALIZES them into a standalone, portable SVG document string ([SvgRenderContext::finish]) — real vector paths, outlined text (via [uzor::shaper::text_to_path], fidelity-first per nemo/docs/uzor-engines/research_export_sota_2026.md §6's own verdict) plus an invisible companion <text> element so the document stays searchable/selectable, and raster images embedded as base64 PNG <image> elements.

Incubating (publish = false), same tier as uzor-export/ uzor-figures/uzor-typeset — API surface not yet stable.

Design notes (report)

• Transforms are baked into every emitted coordinate, not expressed as nested <g transform="..."> scopes per save/restore — simpler (one flat element list, no scope-tracking </g> bookkeeping to keep balanced across arbitrary save/restore nesting) and more portable (plain numeric path/rect coordinates are understood by literally every SVG consumer, whereas relying on nested transform stacking correctly is a strictly harder property to guarantee as more state gets threaded through). The one documented exception is a ROTATED/SKEWED <image> element (draw_image_rgba) — raster content genuinely cannot be expressed as path d coordinates, so that one element carries its own transform="matrix(...)" attribute; every other draw call bakes fully into coordinates. Stroke width / dash arrays / radial-gradient radii are separate SVG attributes (not path geometry) and are scaled by [crate::transform]'s own approximate uniform scale_factor() so they still visually track Painter::scale under a baked transform.
• Text is painted as real outlined glyph paths (kept searchable/selectable via an accompanying opacity="0" <text> element, not embedded/subsetted live fonts) — matches the research doc's "fidelity-first" verdict for this backend's use case (report/chart export) over the alternative "live <text> + embedded WOFF2" strategy (trades outline fidelity for smaller files/native text selection — a plausible follow-up, not built this pass).
• BatchPainter/Effects/UiEffectHelpers are left at their own trait-default bodies — already-documented, non-silent fallbacks: BatchPainter's defaults already loop over this backend's own Painter primitives (this task's own "correct beats clever, loops over the single-ops" instruction — literally free once Painter is real); Effects/UiEffectHelpers have no vector-SVG equivalent attempted this pass (shadow/blend-mode/backdrop-blur).
• GradientPainter IS a real implementation (<linearGradient>/ <radialGradient> defs), not the trait's own flat-fill fallback.
• BackdropBlur (opt-in, not part of the RenderContext supertrait) is not implemented — a raster backdrop-sample blur has no vector-SVG equivalent.