Reject misspelled query language identifiers

[Widthdom]

Summary

• reject unknown --lang spellings with a non-zero E010_USAGE_ERROR and bounded canonical suggestions
• resolve aliases, extensions, and plugin language IDs from the same workspace-aware registry used by indexing
• preserve exact plugin IDs through database filters and validate every effective query root, including workspace databases and batch child databases
• document the behavior in both English and Japanese and add the required changelog fragment

Validation

• dotnet restore CodeIndex.sln
• dotnet build CodeIndex.sln -c Release --no-restore
• full Release test suite: net9 passed; net8 had one unrelated flaky MCP concurrency failure whose isolated reruns passed 3/3
• Issue Reject or suggest misspelled language identifiers #4842 regression tests after the final origin/main merge: net8 15/15, net9 15/15
• dotnet format CodeIndex.sln --no-restore --verify-no-changes
• changelog fragment validation
• Codex adversarial review (two rounds); all findings addressed with regression coverage
• fresh local index and status --check

Follow-up: #4935

Fixes #4842