- Add statement for function-level deferred execution
- Deferred expressions run in LIFO order on function exit (return or implicit)
- Bootstrap: desugar defers in hir_lower.nim (inject before return + end of func)
- Selfhost: emit defers in c_backend.bux via CEmitter defer stack
- Both: add tkDefer token, skDefer AST node, hDefer HIR node
- Parser, lexer, sema, token files updated in both bootstrap/ and src/
- examples/borrow.bux: working borrow expression example
- tests/borrow_test.nim: add 4 new tests for borrow & @[Shared]
- parser.nim: fix borrow parsing order (& before mut)
- Build verified: example compiles and runs