Expose resolved method calls as a CALLS edge

[paracycle]

Goal

Expose method calls in the Cypher graph, resolved to the method declarations they target — so the graph can answer call-graph questions, not just definition/inheritance ones.

What it adds

A new relationship type:

CALLS: Document → Declaration (a Method)

It maps a file's method references to the method declaration each one resolves to, for calls whose receiver type is statically known:

• a constant receiver (Foo.bar), resolved through the receiver's singleton-class ancestry (where class methods live), and
• an implicit self call in a known scope (e.g. calling a sibling method from inside an instance method).

-- Everything a file calls (resolved)
MATCH (d:Document)-[:CALLS]->(m:Method) RETURN d.name, m.name

-- Callers of a specific method
MATCH (d:Document)-[:CALLS]->(m:Method {unqualified_name: 'bar()'}) RETURN d.name

How it resolves

The indexer already records each call with the receiver type's name (the singleton-class name for Foo.bar, the enclosing type for a self call). The schema:

1. resolves that name to a declaration (the same way constant references resolve), then
2. looks the method up along that declaration's ancestry, matching on the base name — method members are keyed name() while call sites record the bare name, so a direct id match doesn't work.

Scope / non-goals

Calls with a dynamic or unknown receiver (foo.bar on a local, a method-chain result, etc.) carry no receiver from the indexer and are intentionally not represented — resolving them would require type inference. This edge covers the statically-resolvable subset only; it's best-effort (first match in ancestry order) rather than a guaranteed runtime target.

The resolver currently lives in the cypher schema (consistent with how it already maps the graph); a future refactor could share a Graph-level method resolver with query.rs's completion path.

Verification

cargo test -p rubydex query::cypher (20 tests, incl. resolution + reverse "who calls this" + that dynamic-receiver calls are excluded); clippy + fmt clean; --schema lists CALLS; full gem suite green.