dwind-dviz: harden the public API

[JedimEmO]

What changed

This PR hardens the new dwind-dviz crate before its first public release. The focus is correctness and extension points, not adding another chart type.

Data and scale contracts

• Add typed DataError validation for empty/duplicate series ids and invalid coordinates.
• Add transactional try_new/try_set constructors for static and mutable sources.
• Add checked logarithmic-scale constructors and duplicate-category validation.
• Add typed CategoryPoint conversion and encode_category_series for categorical bars.
• Make series color assignment deterministic by series id rather than first-render order.

Extensibility and reactivity

• Add CustomScale/CustomScaleHandle for user-defined x/y scales with mapping, inversion, ticks, descriptions, and responsive ranges.
• Add DomainSource for reactive x-extents from static, mutable, and windowed data.
• Make labels and fixed y-domains consistently signal-capable across the presets.
• Add hover and click-selection callbacks to crosshair interaction.

Accessibility and examples

• Keep the chart ARIA fallback and description behavior.
• Provide table_view for series summaries and point_table_view for every exact observation.
• Update the live gallery page and API documentation/roadmap.

Verification

• cargo test -p dwind-dviz-core -p dwind-dviz-data -p dwind-dviz: 72 core, 11 data, and 22 renderer tests passing.
• cargo check --workspace: passing.
• cargo check -p dwind-dviz --target wasm32-unknown-unknown: passing.
• Strict no-dependency Clippy passes for all three dviz crates.
• git diff --check: passing.

Browser tests are configured in CI with wasm-bindgen 0.2.126 to match the lockfile. The local runner is 0.2.128, so local browser execution is blocked by that tool-version mismatch rather than a compile or test failure.