fix: fail schema select on missing columns

[fallintoplace]

Summary

• make Schema::Select() return an error when a requested column name cannot be resolved
• validate TableScanBuilder::Select() during Build() so bad scan projections fail early
• keep manifest reader projection best-effort at its documented boundary by filtering unavailable manifest/data-file columns before calling Schema::Select()
• update schema tests and add table scan coverage for partially missing projections

Tests

• cmake --build build --target schema_test scan_test
• ctest --test-dir build -R 'schema_test|scan_test' --output-on-failure\n- git diff --check\n