GUEST: step 4 — lib/guest/pratt.sx operator-table format + lookup

Extracted the data-half of Pratt-style precedence parsing: the operator
table format and lookup. The climbing loop stays per-language because
the two canaries use opposite conventions (lua: higher prec = tighter;
prolog: lower prec = tighter, with xfx/xfy/yfx assoc tags) — forcing
one shared loop adds callback indirection that obscures more than it
shares. The brief's literal ask is "Grammar is a dict, not hardcoded
cond" and that's what gets shared.

Entry shape: (NAME PREC ASSOC). Three accessors: pratt-op-name /
pratt-op-prec / pratt-op-assoc. One traversal: pratt-op-lookup.

Ported lua/parser.sx — replaced 18-clause cond and the
lua-binop-right? hardcoded `or` with a 15-entry lua-op-table, now
queried via pratt-op-lookup. Ported prolog/parser.sx — pl-op-find
(linear walk reimpl) deleted; pl-op-lookup wraps pratt-op-lookup;
pl-token-op simplified to return the entry directly.

Verification:
- lua/test.sh: 185/185 = baseline.
- prolog/conformance.sh: 590/590 = baseline (timestamp-only diff).

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

lib/lua/test.sh

@@ -30,6 +30,7 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 1)
 (load "lib/guest/lex.sx")
 (load "lib/guest/prefix.sx")
+(load "lib/guest/pratt.sx")
 (load "lib/lua/tokenizer.sx")
 (epoch 2)
 (load "lib/lua/parser.sx")