feat: introduce local-first SVG workbench

docs/ANIMATION.md

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+# Animation
+
+Native SVG animation elements are discovered/countable in source but removed
+from every rendered editing projection, so imported SMIL and event-triggered
+animation cannot execute automatically. Imported scripts are never supported.
+
+Version 0.1.0 implements a deliberately small app-owned animation slice:
+
+- add an opacity animation to the selected element;
+- enable/disable/remove definitions;
+- preview generated CSS only in the opaque-origin canvas;
+- persist definitions in an explicit `.svgtools.json` project;
+- apply validated CSS plus stable target IDs to source in one transaction.
+
+One shared validator is used for project import, preview and Apply. It bounds
+definition/keyframe counts and strings, requires finite ordered offsets and
+bounded timing/iteration values, allowlists property/kind/direction/fill mode,
+accepts only safe easing grammar and parses every CSS value with css-tree. URLs,
+resource functions, structural CSS/XML characters and parser raw nodes are
+rejected even for disabled definitions. Selectors and keyframe identifiers are
+escaped/generated by the app.
+
+The preview has play/pause as an enable toggle but no timeline, seek or native
+SMIL editing. Duration/keyframes are not yet exposed as a general UI. Transform,
+colour, motion-path and compatible path-morph authoring, animation discovery
+panels and conversion between CSS/SMIL remain future milestones. Applying CSS
+changes the SVG source intentionally and may affect downstream consumers that
+do not support the same CSS animation features.