go: parse.sx scaffold — primary expressions + Go precedence table + 17 tests [consumes-pratt consumes-ast]

Starts Phase 2. lib/go/parse.sx defines:
  * go-precedence-table — Go's five operator-precedence levels in the
    (NAME PREC ASSOC) entry shape from lib/guest/pratt.sx, ready for the
    binary-operator iteration to consume via pratt-op-lookup.
  * go-parse(src) — tokenises and parses ONE primary expression: int,
    float, imag, string, rune literals become (ast-literal VALUE);
    identifiers become (ast-var NAME). Built directly on lib/guest/ast.sx
    constructors — no intermediate AST shape.

Conformance.sh extended to load lib/guest/{ast,pratt}.sx and run the
new parse suite. Scoreboard cleanup: drop the "pending" parse row since
the suite is now real.

parse 17/17 (lex still 129/129). Total 146/146.

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

lib/go/conformance.sh

@@ -28,13 +28,18 @@ trap "rm -f $TMPFILE $OUTFILE" EXIT
 # Each suite: name | pass-counter | total-counter
 SUITES=(
   "lex|go-test-pass|go-test-count"
+  "parse|go-parse-test-pass|go-parse-test-count"
 )
 
 cat > "$TMPFILE" <<'EPOCHS'
 (epoch 1)
 (load "lib/guest/lex.sx")
+(load "lib/guest/ast.sx")
+(load "lib/guest/pratt.sx")
 (load "lib/go/lex.sx")
+(load "lib/go/parse.sx")
 (load "lib/go/tests/lex.sx")
+(load "lib/go/tests/parse.sx")
 EPOCHS
 
 idx=0
@@ -99,7 +104,6 @@ cat > lib/go/scoreboard.json <<JSON
   "total_pass": $TOTAL_PASS,
   "total": $TOTAL_COUNT,
   "suites": [$JSON_SUITES,
-    {"name":"parse","pass":0,"total":0,"status":"pending"},
     {"name":"types","pass":0,"total":0,"status":"pending"},
     {"name":"eval","pass":0,"total":0,"status":"pending"},
     {"name":"runtime","pass":0,"total":0,"status":"pending"},
@@ -116,8 +120,7 @@ cat > lib/go/scoreboard.md <<MD
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
-$MD_ROWS| ⬜ | parse | 0 | 0 |
-| ⬜ | types | 0 | 0 |
+$MD_ROWS| ⬜ | types | 0 | 0 |
 | ⬜ | eval | 0 | 0 |
 | ⬜ | runtime | 0 | 0 |
 | ⬜ | stdlib | 0 | 0 |