v0.6.4

[0.6.4] - 2026-05-31

• chore: bump to 0.6.4
• merge: ui.rs split + macOS Finder open into main
• docs(changelog): note ui.rs split into inspector.rs + floating.rs
• docs(ui): note ui_system is now a dispatcher; bodies in sibling modules
• refactor(ui): extract inspector panel into ui/inspector.rs
• refactor(ui): extract menu-pill body into floating::pill_menu_contents
• refactor(ui): extract tool-island body into floating::tool_island_contents
• docs: drop .fbx from supported-format list
• perf(grid): memoize bounding box for per-frame inspector
• perf(canvas): bound origin-triad voxel probe to the origin cube
• refactor(ecs): bundle 8+ arg systems into SystemParam structs
• ci(lint): make clippy a hard gate and clear warnings
• feat(io): track unsaved changes and guard Open/New
• refactor(tools): merge Fill into Paint with double-click flood
• feat(brush): Shift-lock brush stroke to a straight axis
• feat(ui): show real-time shape/selection info in palette panel
• docs: finalize CHANGELOG for v0.6.3 [skip ci]