refactor: consolidate compiler utilities and passes

[zharinov]

Summary

• Extract to_pascal_case and to_snake_case to plotnik-core::utils (fixes behavioral bug where TypeScript emitter produced FOOBAR instead of FooBar for FOO_BAR input)
• Add is_recursive() API to DependencyAnalysis, removing duplicate recursion detection from type_check
• Combine NodeTypeCollector and FieldCollector into single SymbolResolver visitor (3→2 AST passes in link phase)
• Create query/refs.rs with ref_nodes(), collect_ref_names(), contains_ref() utilities

Test plan

• All 689 tests pass
• Clippy clean