Log filter: match case-insensitively

The Log window's filter used a case-sensitive substring match, so "error" missed
"ERROR" -- inconsistent with the rest of the app. Match case-insensitively.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

host/src/log_panel.cpp

@@ -1,7 +1,10 @@
 #include "log_panel.hpp"
 
+#include <algorithm>
+#include <cctype>
 #include <cstdio>
 #include <cstring>
+#include <string>
 
 #include "imgui.h"
 
@@ -11,6 +14,24 @@
 namespace coop
 {
 
+namespace
+{
+// Case-insensitive substring test, so the log filter matches regardless of case (consistent with the
+// rest of the app, where "error" should find "ERROR").
+bool icontains(const std::string& hay, const char* needle)
+{
+	if (needle == nullptr || needle[0] == '\0')
+	{
+		return true;
+	}
+	auto lower = [](std::string s) {
+		std::transform(s.begin(), s.end(), s.begin(), [](unsigned char c) { return static_cast<char>(std::tolower(c)); });
+		return s;
+	};
+	return lower(hay).find(lower(needle)) != std::string::npos;
+}
+} // namespace
+
 void LogPanel::add_line(const LogRecord& rec)
 {
 	if (first_millis_ == 0)
@@ -55,7 +76,7 @@ void LogPanel::draw()
 		const bool has_filter = filter_[0] != '\0';
 		for (const Line& line : lines_)
 		{
-			if (has_filter && line.text.find(filter_) == std::string::npos)
+			if (has_filter && !icontains(line.text, filter_))
 			{
 				continue;
 			}