[CalvinAllen]

Summary

errors_list reported counts that were capped by maxResults, zeroed by the severity filter, and it never set Truncated. This fixes all three.

• Counts cover the whole Error List. The loop no longer stops at maxResults. TotalCount, ErrorCount, WarningCount and MessageCount are counted for every entry, whatever the severity filter. With 250 errors and the default maxResults = 100, the result is now TotalCount: 250, ErrorCount: 250, Truncated: true.
• Truncated is set. It is true when more entries matched than maxResults allowed.
• No placeholder item. When nothing matches, Items is empty with correct counts. The "build to populate the Error List" hint moved into the tool description, which now also explains what the counts and Truncated mean.
• Entries past the cap are counted only. Their full details (text, file, line and so on) are only read for entries that are returned.

The counting and capping logic is now in VisualStudioService.CollectErrorListEntries, a pure method, so it can be unit tested without Visual Studio.

Notes

• The counts come from the Error List table control, so they follow the window's own scope and source filters (for example "Current Project" or "Build Only").
• feature request: more filters for errors_list #111 adds more errors_list filters and will change the same method, so whichever PR merges second will need a rebase.
• symbol_workspace and find_references set Truncated with slightly different logic (one compares the unfiltered symbol count, the other uses >=). They are not changed here.

Testing

• dotnet build src/CodingWithCalvin.MCPServer.slnx: 0 warnings, 0 errors
• dotnet test: 90 passed, including 11 new tests in ErrorListTests.cs covering capped counts, counts under a severity filter, the Truncated boundary, empty results, entries that cannot be read, and reading details only for returned entries
• Not yet run against a live Error List in Visual Studio