feat: add bytecode emit infrastructure

[zharinov]

Summary

• Add query/emit.rs - bytecode emission from TypeContext/LinkedQuery
• Add bytecode/emit/typescript.rs - TypeScript generation from bytecode Module
• Add emit() methods to Query and LinkedQuery
• Add comprehensive tests in emit_tests.rs

This is purely additive - the existing type_check/emit_ts.rs path remains unchanged. A follow-up PR will switch consumers to the new bytecode path.

Test plan

• cargo test -p plotnik-lib --features plotnik-langs passes (602 tests)
• New emit tests verify bytecode structure and TypeScript output