feat: upgrade object literal and keyword errors to Rust-quality

Extended Rust-quality diagnostics to more error paths:

✨ Errors Upgraded:
- Object literal syntax errors ( or identifier)
- Keyword syntax errors ()
- Both now include line + column + helpful examples

📊 Before/After:
BEFORE: "Expected ':key value' or 'identifier' in object literal, got LeftBrace"
AFTER:  "Syntax error at line 12, column 8: Expected `:key value` pair or identifier

        Help: Object syntax:
              {:key value} - key-value pair (requires colon before key!)
              {name} - shorthand for {:name name}
              Example: {:wallet addr :amount 100}"

🧪 Test Results:
All 3 self-healing attempts now show Rust-quality errors:
- Attempt #1: line 36, col 44
- Attempt #2: line 45, col 44
- Attempt #3: line 45, col 45

AI is making progress between attempts (fixing some errors),
but struggling with deeply nested S-expression parenthesis tracking.

Related: #error-diagnostics #self-healing #developer-experience

Author: 0xrinegade

crates/ovsm/src/parser/sexpr_parser.rs

@@ -167,10 +167,12 @@ impl SExprParser {
             // Keywords evaluate to strings with colon prefix
             Ok(Expression::StringLiteral(keyword))
         } else {
-            Err(Error::ParseError(format!(
-                "Expected identifier after ':', got {:?}",
-                self.peek().kind
-            )))
+            Err(self.expected_error(
+                "identifier after `:`",
+                Some("Keyword syntax: :name\n\
+                      Used for object keys: {:name value}\n\
+                      Example: {:wallet \"ABC...\" :amount 100}")
+            ))
         }
     }
 
@@ -922,10 +924,13 @@ impl SExprParser {
                 let value = Expression::Variable(key.clone());
                 pairs.push((key, value));
             } else {
-                return Err(Error::ParseError(format!(
-                    "Expected ':key value' or 'identifier' in object literal, got {:?}",
-                    self.peek().kind
-                )));
+                return Err(self.expected_error(
+                    "`:key value` pair or identifier",
+                    Some("Object syntax:\n\
+                          {:key value} - key-value pair (requires colon before key!)\n\
+                          {name} - shorthand for {:name name}\n\
+                          Example: {:wallet addr :amount 100}")
+                ));
             }
 
             if self.check(&TokenKind::Comma) {