Add SQL, Erlang, and Forth highlighter implementations and tests for LSP process and transport handling.

- Added highlighters for new languages (SQL, Erlang, Forth) with filetype recognition.
- Updated and reorganized syntax files to maintain consistency and modularity.
- Introduced LSP transport framing unit tests and JSON decoding/dispatch tests.
- Refactored `LspManager`, integrating UTF-16/UTF-8 position conversions and robust diagnostics handling.
- Enhanced server start/restart logic with workspace root detection and logging to improve LSP usability.

test_utfcodec.cc

@@ -0,0 +1,101 @@
+// test_utfcodec.cc - simple tests for UtfCodec helpers
+#include <cassert>
+#include <cstdio>
+#include <string>
+#include <string_view>
+
+#include "lsp/UtfCodec.h"
+
+using namespace kte::lsp;
+
+
+static std::string_view
+lp(const std::string &, int)
+{
+	return std::string_view();
+}
+
+
+int
+main()
+{
+	// ASCII: each scalar = 1 UTF-16 unit
+	{
+		std::string s = "hello"; // 5 ASCII
+		assert(utf8ColToUtf16Units(s, 0) == 0);
+		assert(utf8ColToUtf16Units(s, 3) == 3);
+		assert(utf16UnitsToUtf8Col(s, 3) == 3);
+		assert(utf16UnitsToUtf8Col(s, 10) == 5); // clamp to EOL
+	}
+
+	// BMP multibyte (e.g., ü U+00FC, α U+03B1) -> still 1 UTF-16 unit
+	{
+		std::string s = u8"aüαb"; // bytes: a [C3 BC] [CE B1] b
+		// columns by codepoints: a(0), ü(1), α(2), b(3)
+		assert(utf8ColToUtf16Units(s, 0) == 0);
+		assert(utf8ColToUtf16Units(s, 1) == 1);
+		assert(utf8ColToUtf16Units(s, 2) == 2);
+		assert(utf8ColToUtf16Units(s, 4) == 4); // past EOL clamps to 4 units
+
+		assert(utf16UnitsToUtf8Col(s, 0) == 0);
+		assert(utf16UnitsToUtf8Col(s, 2) == 2);
+		assert(utf16UnitsToUtf8Col(s, 4) == 4);
+	}
+
+	// Non-BMP (emoji) -> 2 UTF-16 units per code point
+	{
+		std::string s = u8"A😀B"; // U+1F600 between A and B
+		// codepoints: A, 😀, B => utf8 columns 0..3
+		// utf16 units: A(1), 😀(2), B(1) cumulative: 0,1,3,4
+		assert(utf8ColToUtf16Units(s, 0) == 0);
+		assert(utf8ColToUtf16Units(s, 1) == 1); // after A
+		assert(utf8ColToUtf16Units(s, 2) == 3); // after 😀 (2 units)
+		assert(utf8ColToUtf16Units(s, 3) == 4); // after B
+
+		assert(utf16UnitsToUtf8Col(s, 0) == 0);
+		assert(utf16UnitsToUtf8Col(s, 1) == 1); // A
+		assert(utf16UnitsToUtf8Col(s, 2) == 1); // mid-surrogate -> stays before 😀
+		assert(utf16UnitsToUtf8Col(s, 3) == 2); // end of 😀
+		assert(utf16UnitsToUtf8Col(s, 4) == 3); // after B
+		assert(utf16UnitsToUtf8Col(s, 10) == 3); // clamp
+	}
+
+	// Invalid UTF-8: treat invalid byte as U+FFFD (1 UTF-16 unit), consume 1 byte
+	{
+		std::string s;
+		s.push_back('X');
+		s.push_back(char(0xFF)); // invalid single byte
+		s.push_back('Y');
+		// Columns by codepoints as we decode: 'X', U+FFFD, 'Y'
+		assert(utf8ColToUtf16Units(s, 0) == 0);
+		assert(utf8ColToUtf16Units(s, 1) == 1);
+		assert(utf8ColToUtf16Units(s, 2) == 2);
+		assert(utf8ColToUtf16Units(s, 3) == 3);
+
+		assert(utf16UnitsToUtf8Col(s, 0) == 0);
+		assert(utf16UnitsToUtf8Col(s, 1) == 1);
+		assert(utf16UnitsToUtf8Col(s, 2) == 2);
+		assert(utf16UnitsToUtf8Col(s, 3) == 3);
+	}
+
+	// Position/Range helpers with a simple provider
+	{
+		std::string lines[]   = {u8"A😀B"};
+		LineProvider provider = [&](const std::string &, int line) -> std::string_view {
+			return (line == 0) ? std::string_view(lines[0]) : std::string_view();
+		};
+		Position p8{0, 2}; // after 😀 in utf8 columns
+		Position p16 = toUtf16("file:///x", p8, provider);
+		assert(p16.line == 0 && p16.character == 3);
+
+		Position back = toUtf8("file:///x", p16, provider);
+		assert(back.line == 0 && back.character == 2);
+
+		Range r8{{0, 1}, {0, 3}}; // A|😀|B end
+		Range r16 = toUtf16("file:///x", r8, provider);
+		assert(r16.start.character == 1 && r16.end.character == 4);
+	}
+
+	std::puts("test_utfcodec: OK");
+	return 0;
+}