feat(cyvest-vis): adopt deterministic force-directed layouts

[PakitoSec]

Summary

• replace the ELK/Dagre-based graph layouts in @cyvest/cyvest-vis with deterministic d3-force positioning for observables and investigation views
• refresh node styling, theming, and interactions with neutral surfaces, dark theme support, hover neighborhood focus, and updated canvas controls
• update the demo app and package docs to reflect the new force-directed experience, layout options, and Findings/Evidence rendering

Testing

• update js/packages/cyvest-vis/tests/observables.test.ts to cover deterministic force positions, restrained level colors, and compact investigation node styling