Redesign data flow and entity workflows

[jakthom]

Summary

• adopt Tailwind CSS v4 and Basecoat while keeping the compiled UI assets embedded and offline
• redesign the data-flow graph with compact three-lane cards, a bounded centered panel, dotted one-second edge flashes, and a separated unused-endpoints row
• keep disabled components in the main graph and mute unused sinks without hiding their live health state
• move source, sink, and connector creation and editing into dialogs with generated IDs, consistent overview panels, and overview delete actions
• improve source-device table spacing, responsive behavior, color hierarchy, and browser coverage

Testing

• go test ./...
• npm test
• npm run build:css
• git diff --check