Fix parser bug: string values like ")" were confused with delimiter tokens

Both Python and JS parsers used next_token() which returns plain strings
for both delimiter characters and string values, making them
indistinguishable. A string whose value is ")" or "(" would be
misinterpreted as a structural delimiter, causing parse errors.

Fix: use peek() (raw character) for all structural decisions in
parseExpr before consuming via next_token(). Also add enhanced error
logging to sx.js mount/loadComponents for easier future debugging.

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

shared/sx/parser.py

@@ -208,17 +208,25 @@ def parse_all(text: str) -> list[Any]:
 
 
 def _parse_expr(tok: Tokenizer) -> Any:
-    token = tok.next_token()
-    if token is None:
+    # Use peek() (raw character) for structural decisions so that string
+    # values like ")" or "(" don't get confused with actual delimiters.
+    raw = tok.peek()
+    if raw is None:
         raise ParseError("Unexpected end of input", tok.pos, tok.line, tok.col)
-    if token == "(":
+    if raw in ")]}":
+        tok.next_token()  # consume the delimiter
+        raise ParseError(f"Unexpected {raw!r}", tok.pos, tok.line, tok.col)
+    if raw == "(":
+        tok.next_token()  # consume the '('
         return _parse_list(tok, ")")
-    if token == "[":
+    if raw == "[":
+        tok.next_token()  # consume the '['
         return _parse_list(tok, "]")
-    if token == "{":
+    if raw == "{":
+        tok.next_token()  # consume the '{'
         return _parse_map(tok)
-    if token in (")", "]", "}"):
-        raise ParseError(f"Unexpected {token!r}", tok.pos, tok.line, tok.col)
+    # Everything else: strings, keywords, symbols, numbers
+    token = tok.next_token()
     return token