diff: ghost changed/removed edges + surface config-string dependencies

[lex00]

Context

The composite-tier diff (#49) classifies and paints nodes (added/removed/changed/same) and renders the union so removed nodes ghost. Two gaps remain on the edge / dependency side.

1. Edge diff status

unionGraph already carries removed edges, but the renderer doesn't style edges by diff status — a removed or added edge draws like any other line. Classify edges (added/removed/same by from→to[→viaAttr]) and paint them (removed = red dashed/ghost, added = green) the way nodes are.

2. Config-string dependencies aren't graph edges

A real dependency expressed only as a config string never becomes a ref, so it's invisible at every tier and in the diff. Concretely: FargateAlb({ environment: { DB_HOST: db.endpoint } }) produced no app→db edge — db.endpoint resolved to a value, not a tracked ref. So "the app now talks to the DB" doesn't surface.

Options to explore (likely needs chant-side support):

• chant tracks AttrRefs even when embedded in string values / environment maps, emitting them as edges (with the consuming attr as viaAttr).
• or pinhole heuristically scans attr values for resolved refs — fragile, probably wrong place.

This is a known limit of diagramming intent: logical links hidden in config strings aren't in the graph.

Related: #49, #3.

[lex00]

Edge-ghosting shipped via #57: added edges green, removed edges red-ghosted, classified by diffEdges across the composite + member tiers. The remaining half of this issue — surfacing config-string dependencies (a ref hidden in an env-var string like DB_HOST: db.endpoint never becomes a graph edge) — is not fixable in pinhole alone; it needs chant to emit AttrRefs embedded in string/map values. Leaving this issue open scoped to that chant-side dependency.