refactor: restructure CLI commands

[zharinov]

Summary

Restructure CLI from monolithic debug/types commands to focused single-purpose commands:

Old	New	Purpose
debug -s	tree	Explore tree-sitter AST
debug -q	check	Validate query (silent on success)
debug -q --bytecode	dump	Show compiled bytecode
types	infer	Generate TypeScript types

Also extracts shared utilities:

• lang_resolver.rs - Language detection from file extensions
• query_loader.rs - Query loading from file or inline

Depends on #201 (uses codegen::typescript)

Test plan

• cargo test -p plotnik-cli passes (14 tests)
• CI passes