Fix SQL generated-column reference persistence

[Widthdom]

Summary

• register the SQL generated_column_dependency reference kind emitted for generated/computed-column expressions
• add regression coverage that every reference produced by the existing generated-column fixture is registered
• document the reference kind and add a bilingual changelog fragment

Root cause

SqlReferenceExtractor emitted generated_column_dependency, but SymbolKindCatalog.ReferenceKinds did not contain it. DbWriter.ValidateReferenceKinds therefore rejected the extracted reference batch with ArgumentException during persistence.

The existing schema-refresh path derives its CHECK constraint from SymbolKindCatalog, so existing databases are upgraded through the normal constraint-currentness migration.

Validation

• generated-column regression test: passed on net8.0
• ReferenceExtractorTests + DbSchemaConstraintTests: 1,272 passed
• full solution suite completed on net8.0 and net9.0; three unrelated load-sensitive tests timed out/flaked while several worktrees were testing concurrently, then all three passed in isolated reruns on both TFMs (3/3 each)
• Debug build: 0 warnings, 0 errors
• changelog validation: 83 fragments validated
• post-commit index refresh: 0 warnings, 0 errors; reference graph complete
• status --check: workspace matches index, no failed checks

Documentation and changelog

• added the kind to both English and Japanese reference-taxonomy tables in DEVELOPER_GUIDE.md
• added changelog.d/unreleased/+sql-generated-column-reference-kind.fixed.md

No open GitHub issue matched this failure, so this PR intentionally has no Fixes #... line.

Follow-up candidates

• None.