Clarify node visual hierarchy and compact arrows

[teloverge]

Summary

• derive active-work priority from literal in-progress, claimed/assigned fallback, ready-for-agent, and blocked/terminal states
• render dimensional Canvas issue spheres with at most one status ring plus one selection ring
• prioritize selected and CURRENT labels, preserve direct-only selected edge emphasis, and shrink all arrowheads to shared compact geometry
• add reduced-motion wiring and document the visual grammar

Validation

• bun.exe run test (217 tests)
• bun.exe run check
• bun.exe run build
• cargo.exe fmt --all -- --check
• cargo.exe clippy --workspace --all-targets --locked -- -D warnings
• cargo.exe test --workspace --locked -- --test-threads=1
• native release binary launched and visually inspected on Windows, including a selected ready-for-agent node