feat: introduce local-first SVG workbench

docs/ACCESSIBILITY.md

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+# Accessibility audit
+
+The audit is evidence-based and intentionally narrower than a browser or
+assistive-technology accessible-name computation.
+
+Implemented checks include:
+
+- root accessible name evidence from direct `title`, `aria-label` or a uniquely
+  resolved `aria-labelledby` target;
+- missing root description (`desc`/`aria-describedby` evidence);
+- missing, duplicate or ambiguous ARIA ID references;
+- focusable graphical/link elements without local naming evidence;
+- selected fill/stroke contrast evidence where simple literal colours can be
+  evaluated;
+- reference diagnostics that can invalidate accessible relationships.
+
+Findings identify severity, rule, evidence, limitation and a suggested fix.
+Safe automatic fixes insert a root `title` or `desc` through an exact source
+patch, preserve surrounding source and are undoable.
+
+Limitations: the audit does not compute CSS cascade, rendered visibility,
+language, reading order, browser/AT mappings, text contrast over arbitrary
+backgrounds, keyboard interaction quality or author intent. It does not certify
+WCAG conformance. Generated placeholder title/description text must be replaced
+with an author-appropriate description and tested with target browsers and
+assistive technology.