Implements DuckDB-style SELECT * EXCLUDE (columns...) syntax for cleaner
column exclusion without manually listing all desired columns.

Key Changes:
- Parser: Added EXCLUDE token and parsing logic for * EXCLUDE (col1, col2, ...)
- AST: New SelectItem::StarExclude variant with excluded_columns list
- Query Engine: Expansion logic that filters out excluded columns at execution time
- Examples: Complete demo file with security, performance, and readability use cases

Features:
✓ Case-insensitive column matching
✓ Works with WHERE, ORDER BY, LIMIT, GROUP BY clauses
✓ Handles nonexistent columns gracefully (silently ignores)
✓ Table-qualified syntax support (future: table.* EXCLUDE)
✓ Multiple exclusions in single statement

Benefits:
- Security: Easy to exclude sensitive columns (passwords, SSNs, etc.)
- Performance: Skip large BLOB/TEXT columns when not needed
- Maintainability: New columns auto-included without query updates
- Readability: Clearer intent than listing 50+ columns manually

Implementation Notes:
- No transformer needed - expansion happens in query engine
- Reuses existing column resolution infrastructure
- Pattern matches all SelectItem match arms for completeness
- 10 files modified, comprehensive example suite added

Examples:
SELECT * EXCLUDE (password, created_at) FROM users;
SELECT * EXCLUDE (eccentricity, albedo) FROM solar_system WHERE type = 'Planet';

Completes roadmap item #10 (SELECT * EXCLUDE) - v1.66.0
Next: SELECT * REPLACE for column value transformation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>