fix: resolve CALLS edge targets to qualified names at parse time

[madinal]

Summary

CALLS edges were broken in three ways, causing callers_of, callees_of, impact radius, and dependent-file queries to silently return empty or incomplete results:

1. Bare target names — CALLS edges stored bare function names (func_name) while all graph queries match by qualified name (file.py::func_name). Added parse-time resolution using import mappings and cached module-to-file-path lookup (Python + JS/TS). Unresolvable targets (method calls, builtins) gracefully fall back to bare names.

2. Decorated functions invisible to same-file resolution — _collect_file_scope only checked direct root.children types, missing functions wrapped in decorated_definition AST nodes (any function with a decorator). These were absent from defined_names, so same-file call resolution silently failed for them.

3. Multiple call sites collapsed into one edge — upsert_edge() deduped on (kind, source, target, file_path) without line, so multiple calls to the same function from the same caller were collapsed into a single edge. Adding line to the lookup preserves each distinct call site.

Test plan

• test_calls_edge_same_file_resolution — same-file calls are qualified
• test_calls_edge_cross_file_resolution — imported call targets resolve to the defining file
• test_unresolved_calls_stay_bare — method calls remain bare (no false resolution)
• test_calls_edge_decorated_function_resolution — decorated functions resolve as same-file call targets
• test_multiple_calls_to_same_function — multiple calls on different lines produce distinct edges
• test_upsert_edge_preserves_multiple_call_sites — DB layer stores both edges
• All existing tests pass unchanged

🤖 Generated with Claude Code

[tirth8205]

Very useful improvement — qualified names for CALLS edges + handling of decorators is great.
Critical fix needed:
• Current module file cache key (language:module) ignores caller directory → relative imports from different folders will collide. Include file_path parent in the cache key.
Once fixed this is merge-ready.
Thanks for the PR — planning to merge in the next few days!

[tirth8205]

Merged to main via manual squash-merge with cache key fix. Thank you @madinal!