Koru lands template-based metaprogramming

Moving metaprogramming from compiler internals to userland templates is a radical simplification that prioritizes portability and AI readability.

• –Shifting to templates reduces compiler complexity from O(Nodes × Languages) to O(Languages), making new backend support a trivial exercise.
• –The "Effect-Branch Engine" and "Phantom Obligations" provide zero-cost safety, tracking resource states without the overhead of a garbage collector.
• –Explicit event contracts and monadic flow align with an "AI-first" design, producing code that is easier for models to reason about and generate.
• –Replacing 450 lines of AST-manipulation with a single 6-line template demonstrates the power of treating control flow as a userland primitive.