Only treat 'bin'/'obj' as build artifact path segments and add related test

[sharpninja]

Motivation

• Prevent skipping files when directory names merely contain the substrings "bin" or "obj" rather than being build artifact directories.
• Make file enumeration robust across platforms by checking path segments instead of performing substring matches on full paths.

Description

• Replace substring checks for bin/obj with a new helper IsBuildArtifactPath(string relativePath) that splits the relative path into segments and matches segments case-insensitively.
• Compute relativePath via Path.GetRelativePath(dir, path) and use it to decide whether a file is in a bin/obj segment; retain existing exclusions for hidden files and mcp.db.
• Apply the same change in both src/McpServer.Services/Ingestion/RepoIngestor.cs and src/McpServer.Support.Mcp/Ingestion/RepoIngestor.cs and add a unit test in tests/McpServer.Support.Mcp.Tests/Ingestion/RepoIngestorTests.cs.

Testing

• Added unit test IngestAsync_DoesNotSkipPathsThatContainBinOrObjAsSubstring and adjusted IngestAsync_SkipsLargeFiles to run under the test harness.
• Ran the test suite with dotnet test for the McpServer.Support.Mcp.Tests project and the tests completed successfully.
• Existing ingestion tests including IngestAsync_ContentHash_DeterministicForSameContent also passed.

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Codex Task