refactor: reorganize compiler

[zharinov]

Summary

Reorganizes plotnik-lib into a professional compiler structure with clear phase boundaries:

• analyze/ - Semantic analysis (symbol_table, dependencies, type_check, validation)
• compile/ - Thompson NFA construction (AST → IR)
• emit/ - Bytecode emission (IR → binary)
• typegen/ - Type declaration extraction (bytecode → .d.ts)

Pipeline

parser/ → analyze/ → compile/ → emit/ → bytecode binary
                                              ↓
                                        typegen/ → .d.ts

Changes

• Move semantic analysis from query/ to analyze/
• Promote query/compile/ to top-level compile/
• Create emit/ from query/codegen.rs + bytecode/layout.rs
• Rename codegen/ → typegen/ (clarifies it extracts types from bytecode, not codegen in the traditional compiler sense)
• Update AGENTS.md with new project structure
• Delete completed docs/wip/big-bang-refactor.md

Test plan

• All 660 tests pass
• No clippy warnings
• Module documentation updated