Add import-graph / call-graph analysis to domain and hotspot detection

[ivklgn]

Paths updated for v0.7.0 — the detection catalogs moved from skills/init/lib/ to skills/_shared/grounding/. The heuristics are unchanged.

Problem

/archcore:init detection is heuristic. plugins/archcore/skills/_shared/grounding/detect-hotspots.md ranks by lines-of-code, test ratio and grep-style fan-in; detect-domains.md uses directory conventions. Without a real import/call graph, hotspot ranking and domain boundaries are approximations — and both feed decisions the user then lives with: which modules get a spec, and how a large repo is carved into domains.

Expected result

Real dependency-edge analysis (import/call graph, via per-language parsers) feeding hotspot ranking (true fan-in) and domain-boundary detection.

Constraint

detect-* catalogs are pinned by test/structure/init-skill.bats to "lead high-level and mark lists non-exhaustive" — the universality invariant that no depth or language adds a stack-specific detection heuristic. Any graph work must keep detection language-agnostic at the catalog level, with parsers as pluggable evidence rather than branching prose.

Impact

Sharper, more accurate first-day maps for larger and polyglot codebases — but large and language-specific, so best scoped as a design spike plus a one-language pilot rather than a single change.

Proposed approach

• Design spike: graph model + integration points into detect-hotspots / detect-domains, without breaking the non-exhaustive catalog invariant.
• Pilot one language, then add parsers incrementally.

Acceptance criteria

• A pilot language builds a real import graph that measurably improves hotspot/domain output vs. the heuristics, on a fixture where the heuristic answer is known to be wrong.
• init-skill.bats universality tests stay green.

References

Design rationale: .archcore/plugin/bootstrap-scale-modes.plan.md and magic-first-day-init.plan.md (both "Out of scope"). Roadmap-optional. Code: plugins/archcore/skills/_shared/grounding/detect-{hotspots,domains}.md.