fix: collapse tautological err check on lexBarePlaceholder (FP-11)

lexBarePlaceholder has no return-nil path — an unquoted '<' is always
a parse error by design (PT-02(b)) — so `if err := ...; err != nil`
at the call site was flagged by staticcheck (SA4023: always-true
comparison) as pre-existing tech debt blocking the required Lint CI
check on main (confirmed unrelated to FP-10/#265/#266).

Collapses to a direct `return l.lexBarePlaceholder()` — behaviorally
identical, since err was always non-nil anyway.

Author: pbertsch

internal/parser/lexer.go

@@ -100,9 +100,10 @@ func (l *Lexer) nextLine() error {
 				return err
 			}
 		case ch == '<':
-			if err := l.lexBarePlaceholder(); err != nil {
-				return err
-			}
+			// lexBarePlaceholder has no success path — an unquoted '<' is
+			// always a parse error (see its doc comment) — so there's
+			// nothing to fall through to here.
+			return l.lexBarePlaceholder()
 		case ch == ':':
 			l.emit(TOKEN_COLON, ":")
 			l.pos++