go: eval.sx — method dispatch + unary + e2e programs + 14 tests; Phase 4 bar crossed [nothing]

Phase 4 cont. The crossings:

  * Method dispatch — Methods record under #method/TYPE/NAME (same
    mangled-key scheme the type checker uses, intentionally so eval
    and type checker can converge on a shared method-table protocol
    later). go-eval-method-call: lookup the receiver type's method,
    bind receiver param to the struct value, evaluate body. Value and
    pointer receivers treated the same in v0 (pointer semantics not
    modelled yet).
  * Method-call dispatch — In go-eval's :app branch, head=:select
    routes to go-eval-method-call. If the receiver is not a struct,
    falls back to the field-as-callable path.
  * Unary prefix ops — go-eval's :app branch checks for 1-arg :var
    head with op name "-" / "+" / "!". (Other unary ops like
    *p / &v / <-ch / ^x deferred until pointer / channel / bitwise
    semantics arrive.)

End-to-end programs verified:
  * recursive fib(10) = 55
  * struct + method + iterative loop (counter bump 7 times)
  * linear search (returns index or -1)
  * factorial via method on Counter (= 120)
  * count odd numbers in 1..10 = 5

**Phase 4 acceptance bar (80+) crossed: eval 80/80, total 457/457.**

Remaining Phase 4 work (closures, multi-return, full slice triple,
pointer semantics) refines but doesn't gate Phase 5 (goroutines).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/go/scoreboard.md

@@ -1,13 +1,13 @@
 # Go-on-SX Scoreboard
 
-**Total: 443 / 443 tests passing**
+**Total: 457 / 457 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
 | ✅ | lex | 129 | 129 |
 | ✅ | parse | 176 | 176 |
 | ✅ | types | 72 | 72 |
-| ✅ | eval | 66 | 66 |
+| ✅ | eval | 80 | 80 |
 | ⬜ | runtime | 0 | 0 |
 | ⬜ | stdlib | 0 | 0 |
 | ⬜ | e2e | 0 | 0 |