go: parse.sx — type assertion v.(T) + minimal type parser + 9 tests [nothing]

Postfix '.' branch now peeks at the next token to disambiguate:
  .ident   →  selector / member access  (list :select OBJ "field")
  .(TYPE)  →  type assertion            (list :assert OBJ TYPE)

New gp-parse-type covers the minimum types needed for assertions:
  name        →  (list :ty-name "int")
  pkg.Name    →  (list :ty-sel "pkg" "Name")
  *T  / **T   →  (list :ty-ptr (list :ty-ptr ...))

Full type grammar — slice []T, array [N]T, map[K]V, chan, func,
struct, interface — is a separate Phase 2 sub-deliverable.

Type AST shapes are Go-specific tagged lists; the canonical AST kit
has no type-system primitives at all yet. Worth a richer kit
discussion once Phase 3 (bidirectional type checker) lands and the
sister plan static-types-bidirectional has a real surface to react to.

parse 70/70, total 199/199.

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

lib/go/scoreboard.md

@@ -1,11 +1,11 @@
 # Go-on-SX Scoreboard
 
-**Total: 190 / 190 tests passing**
+**Total: 199 / 199 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
 | ✅ | lex | 129 | 129 |
-| ✅ | parse | 61 | 61 |
+| ✅ | parse | 70 | 70 |
 | ⬜ | types | 0 | 0 |
 | ⬜ | eval | 0 | 0 |
 | ⬜ | runtime | 0 | 0 |