Graph queries conflate common method names across types

[Widthdom]

Evidence

• Local index was fresh on b9ac272c7b5fa501be07458899524552852dbf2d.
• cdidx hotspots --path src/ --exclude-tests --json --limit 80 ranks common method names as top hotspots: GetString in LspServer.cs with 1684 refs, ToList in FileIndexer.cs with 568 refs, and NewGuid in HttpMcpTransport.cs with 444 refs.
• cdidx callers GetString returns callers that are using unrelated APIs such as reader.GetString, JsonElement.GetString, and similar methods.
• cdidx callers ToList maps ordinary LINQ .ToList() call sites to a FileIndexer symbol.
• cdidx callers NewGuid maps Guid.NewGuid() call sites to a local NewGuid symbol.

Impact

Graph results and hotspot rankings become misleading for common member names. This makes callers, callees, inspect, and hotspots less reliable on real C# codebases.

Expected

Graph resolution should use receiver/type/container/metadata target signals enough to avoid merging unrelated methods that share only a short name. When resolution is ambiguous, results should surface ambiguity instead of attributing the call to a concrete unrelated symbol.

[Widthdom]

Work started on branch fix-issue2818-2831.