Add Docker support for Linux build testing

- Introduced a `Dockerfile` for setting up a minimal Ubuntu-based build environment with required dependencies.
- Added `docker-build.sh` script to simplify Linux build and test execution using Docker or Podman.
- Updated `DEVELOPER_GUIDE.md` with instructions for using Docker/Podman for Linux builds, including CI/CD integration examples.

tests/Test.h

@@ -57,7 +57,9 @@ template<typename A, typename B>
 inline void
 assert_eq_impl(const A &a, const B &b, const char *ea, const char *eb, const char *file, int line)
 {
-	if (!(a == b)) {
+	// Cast to common type to avoid signed/unsigned comparison warnings
+	using Common = std::common_type_t<A, B>;
+	if (!(static_cast<Common>(a) == static_cast<Common>(b))) {
 		std::ostringstream oss;
 		oss << file << ":" << line << ": ASSERT_EQ failed: " << ea << " == " << eb;
 		throw AssertionFailure{oss.str()};
@@ -72,4 +74,4 @@ assert_eq_impl(const A &a, const B &b, const char *ea, const char *eb, const cha
 
 #define EXPECT_TRUE(x) ::ktet::expect((x), #x, __FILE__, __LINE__)
 #define ASSERT_TRUE(x) ::ktet::assert_true((x), #x, __FILE__, __LINE__)
-#define ASSERT_EQ(a,b) ::ktet::assert_eq_impl((a),(b), #a, #b, __FILE__, __LINE__)
+#define ASSERT_EQ(a,b) ::ktet::assert_eq_impl((a),(b), #a, #b, __FILE__, __LINE__)

tests/test_migration_coverage.cc

@@ -424,7 +424,7 @@ TEST (Migration_SyntaxHighlighter_Pattern)
 			break; // Should never happen
 		}
 		std::string line = buf.GetLineString(row);
-		EXPECT_TRUE(line.size() >= 0); // Always true, but validates access
+		// Successfully accessed line - size() is always valid for std::string
 	}
 }