feat: rework studio and add HTML authoring front-end

[LeadcodeDev]

Summary

Two major workstreams landed on this branch:

Studio rework (Dioxus)

• Rebuilt the studio into feature modules (library home, editor, topbar, theme switching) with per-scenario thumbnails
• Property inspector with typed per-family controls (sliders, segmented groups, color swatches, font-weight select, bold/italic toggles) and JSON write-back with debounce
• Content editing for selected elements, including HTML-dialect sources via set_text_content
• Annotations: capture comments on elements, list them in a panel, and an apply-annotations skill for agents to resolve them
• Shared Button and new Textarea components themed on the --rm-* palette
• Full JSON-pointer hit-map from canvas clicks down to source nodes; canvas resizes when the sidebar opens

HTML/CSS authoring front-end

• New rustmotion-html crate: transpiles <rustmotion>/<scene> HTML with inline CSS into scenario JSON (browserless, html5ever-based)
• Maps HTML containers/text elements and generic rm-* custom elements to component JSON
• .html input routed through load_input in the CLI and library loader

Fixes

• Accept container as serde alias of div (restores all_components_deserialize)
• Warn on animation placed at component top level; move showcase animations into style

Test plan

• cargo test — 127 tests pass across all crates

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