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