add generic class and function support

[cs01]

Summary

Adds generic class and function support via type erasure (T → i8*). No monomorphization — all type parameters erase to opaque pointers at the LLVM IR level, keeping codegen simple and self-hosting compatible.

Generic classes:

• class Stack<T>, Box<T>, Queue<T>, Pair<A, B>, Wrapper<T extends Printable> all work
• T[] erases to %ObjectArray*; push/pop/shift guarded against generic class instances to avoid dispatching to built-in array handlers
• new Stack<Point>(), new Box<Animal>() — interface and class type args supported
• type Point = { ... } type alias works as a generic type arg (treated as interface)

Generic functions:

• identity<T>, first<T>(arr: T[]) — type parameter return types infer correctly for both locals and globals
• Compile-time error emitted when generic method return is used without a type annotation

Self-hosting fixes:

• Removed block scope { } from case "type_alias_declaration" in native transformer — the native compiler's break inside a block scope exited the block rather than the switch, silently dropping all type alias declarations from the AST
• Fixed FunctionNode struct layout crash in native compiler
• Moved typeParameters to end of interfaces (CLAUDE.md rule improve install scripts #3); refactored union-type-checker

Tests: 9 new fixtures in tests/fixtures/generics/ — all pass with both node and native compilers. Stage 0 and Stage 1 self-hosting pass (npm run verify:quick).

Limitations (not in this PR)

• Numeric type params (new Stack<number>()) not supported — double and i8* have different sizes
• Generic method returning its own swapped type params (e.g. swap(): Pair<B,A>) — result not tracked as class instance
• No generic constraints beyond single extends clause

Test plan

• npm test — 396+ tests pass (5 pre-existing network failures unrelated to generics)
• All 9 generics fixtures pass: stack, queue, box, pair, generic-functions, generic-interface, generic-type-alias, generic-class-arg, generic-extends
• npm run verify:quick — Stage 0 and Stage 1 self-hosting pass