fix: emit calls edges for Solidity modifier invocations (AGE-4)

[saldestechnology]

Summary

Solidity modifier applications (function f() external onlyOwner) produced no edge in the code graph, so ctx query callers onlyOwner, ctx query impact, and v1.edges could not answer access-control / reentrancy-guard questions — a core audit surface.

Note: modifier definitions were already emitted as symbols (extract_function handles FunctionTy::Modifier). The only gap was the edge from a function to the modifier it applies, because func.attributes was only inspected for visibility and FunctionAttribute::BaseOrModifier was never matched.

Change

• New extract_modifier_edges in src/parser/solidity.rs, invoked for both contract-member and free functions during the call-edge pass. For each FunctionAttribute::BaseOrModifier(_, base) it:
  • takes the modifier/base name (last segment of the IdentifierPath),
  • resolves source_id via the existing func_ranges line lookup,
  • resolves target_id against the modifier's Function symbol (so the edge participates in fan_in/impact traversal, which only follows kind='calls' edges with non-null target_id),
  • pushes an EdgeKind::Calls edge.
• Reuses SymbolKind::Function and EdgeKind::Calls — no model, Cargo, or query-layer changes.
• Also covers constructor base-contract invocations (constructor() Ownable(msg.sender)), emitting an edge with target_id resolved when a matching symbol exists, None otherwise (mirroring unresolved calls).

Tests

Extends test_parse_constructor_and_modifiers to assert a calls edge to onlyOwner exists with target_id resolved to the modifier symbol.

• cargo fmt --all -- --check ✅
• cargo clippy --all-targets -- -D warnings ✅ (0 warnings)
• cargo test ✅ (303 lib + all integration suites pass, 0 failures)

Refs AGE-4. Sibling of AGE-2 (duplicates skip Solidity) and AGE-5 (qualified-call resolution).