Add theorem prover docs page with Phase 2 constraint solving

- prove.sx Phase 2: bounded model checking with 34 algebraic properties
  (commutativity, associativity, distributivity, inverses, bounds, transitivity)
- prove.sx generates SMT-LIB for unbounded Z3 verification via z3-expr
- New docs page /plans/theorem-prover with live results (91/91 sat, 34/34 verified)
- Page helper runs both proof phases and returns structured data
- Parser: re-add ' quote syntax (removed by prior edit)
- Load prove.sx alongside z3.sx at startup

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/parser.py

@@ -309,7 +309,11 @@ def _parse_expr(tok: Tokenizer) -> Any:
     if raw == "{":
         tok.next_token()  # consume the '{'
         return _parse_map(tok)
-    # Quasiquote syntax: ` , ,@
+    # Quote / quasiquote syntax: ' ` , ,@
+    if raw == "'":
+        tok._advance(1)  # consume the quote
+        inner = _parse_expr(tok)
+        return [Symbol("quote"), inner]
     if raw == "`":
         tok._advance(1)  # consume the backtick
         inner = _parse_expr(tok)