feature: add build script and update .gitignore

Add build.bat for compiling WASURO with FPC 3.2.2 (x86_64-win64).
Supports optional "test" argument to enable the test suite.

build.bat:
- Configures FPC with all source unit paths (emu, wasm, parser,
  sections, types, vm, test infrastructure)
- Outputs to bin/WASURO.exe, intermediate units to lib/
- "build.bat test" passes -dRUN_TESTS to include test units
- Debug info enabled (-gw3)
- Propagates FPC exit code on failure

.gitignore:
- Add AGENTS.md (AI agent instructions, not project source), this file
should be personal choice, not dictated at a project level.

.gitignore

@@ -1,2 +1,3 @@
 bin
 lib
+AGENTS.md

build.bat

@@ -0,0 +1,39 @@
+@echo off
+setlocal
+
+set ROOT=%~dp0
+set SRC=%ROOT%src
+set BIN=%ROOT%bin
+set LIB=%ROOT%lib
+set FPC=C:\Lazarus\fpc\3.2.2\bin\x86_64-win64\fpc.exe
+
+set TESTFLAGS=
+if "%1"=="test" set TESTFLAGS=-dRUN_TESTS
+
+if not exist "%BIN%" mkdir "%BIN%"
+if not exist "%LIB%" mkdir "%LIB%"
+
+"%FPC%" ^
+  %TESTFLAGS% ^
+  -FE"%BIN%" ^
+  -FU"%LIB%" ^
+  -Fu"%SRC%\emu" ^
+  -Fu"%SRC%\wasm" ^
+  -Fu"%SRC%\wasm\parser" ^
+  -Fu"%SRC%\wasm\parser\sections" ^
+  -Fu"%SRC%\wasm\test" ^
+  -Fu"%SRC%\wasm\test\opcodes" ^
+  -Fu"%SRC%\wasm\test\parsers" ^
+  -Fu"%SRC%\wasm\test\infra" ^
+  -Fu"%SRC%\wasm\types" ^
+  -Fu"%SRC%\wasm\vm" ^
+  -gw3 ^
+  -o"%BIN%\WASURO.exe" ^
+  "%SRC%\project\WASURO.lpr"
+
+if %ERRORLEVEL% NEQ 0 (
+    echo Build failed with error code %ERRORLEVEL%
+    exit /b %ERRORLEVEL%
+)
+
+echo Build succeeded: %BIN%\WASURO.exe