Add interactive semantic diff graph explorer

[forhappy]

What changed

• replace the dense semantic-diff graph with a bounded, collision-free capsule layout
• add a persistent node inspector with incoming/outgoing relationships, related findings, and source-patch navigation
• highlight the selected node and its connected topology while dimming unrelated nodes and edges
• add keyboard controls, responsive stacking, reduced-motion support, and a safe no-JavaScript/runtime fallback
• sample changed, added, and removed nodes fairly so every non-empty change category is visible
• keep exhaustive node/edge lists and embedded JSON as the authoritative complete result

Why

The previous force-directed visualization produced overlapping labels and was difficult to inspect. Its status-priority truncation could also fill the visual sample with changed and removed nodes before any added nodes were rendered, even when the report contained many additions.

This makes the standalone semantic-diff report practical for understanding code evolution beyond line-level diffs while preserving deterministic, bounded rendering performance.

Validation

• cargo fmt --all -- --check
• cargo clippy -p compass-cli --all-targets --no-deps -- -D warnings
• focused semantic-diff renderer and CLI integration tests
• cargo test --workspace
• 4 Chromium Playwright interaction tests
• fresh CocoIndex report generated from 9057153 to 71f9cc9
• real report visual sample verified as 17 added, 16 removed, 9 changed, 42 total
• deterministic semantic-diff JSON verified across repeated runs
• graphify update .