Emphasize selected node connections

[teloverge]

Summary

• emphasize only direct incoming and outgoing edges for selected nodes
• render selected connections last with stronger strokes and arrows while retaining semantic styling and motion
• add mutation-resistant canvas coverage for direct scope, ordering, deselection, stale selection, and workflow arrows
• document the design and implementation plan, and add an Unreleased changelog entry

Why

Selected nodes already had a node ring and camera treatment, but their immediate graph relationships were not easy to trace. This adds local visual emphasis without changing topology, transitive path analysis, or workflow meaning.

Impact

Selecting a node makes its direct dependency and parent/subissue connections easier to follow. Deselecting restores the ordinary graph treatment; unrelated and transitive edges retain their existing context treatment.

Validation

• C:\Users\pfdev\.vite-plus\bin\npm.exe --prefix web test — 206 passed
• C:\Users\pfdev\.vite-plus\bin\npm.exe --prefix web run check — 0 errors, 0 warnings
• C:\Users\pfdev\.vite-plus\bin\npm.exe --prefix web run build
• cargo.exe fmt --all -- --check
• cargo.exe clippy --workspace --all-targets --locked -- -D warnings
• cargo.exe test --workspace --locked -- --test-threads=1
• independent code review — no remaining findings