[ClausValcaTD]

Summary

Fixes two problems reported in #176: xdelta patching fails on Windows, and the app's info/About tab shows 3.0.0 instead of the real version.

Closes #176.

Root cause

1. xdelta3 was never found. AppConfig.xdelta3Path (gui/lib/utils/config.dart) hard-coded a path next to the main executable (<exeDir>/xdelta3.exe) and ignored the bundled assets/ folder. In a real install, xdelta3.exe ships under assets/windows/…, so every xdelta patch failed with "xdelta3 binary not found".

2. The version was hard-coded. core/bin/openrom.dart (--version) fell back to a literal 'v3.0.0', and the About screen reads that via CoreBridge.getVersion() — hence "3.0.0".

Changes

xdelta3 resolution

File	Change
gui/lib/utils/config.dart	AppConfig.getToolPath now delegates to the core's core.getToolPath(), i.e. the standard chain: config.json override → bundled assets/<os>[/<arch>]/<tool> → OS PATH
core/lib/src/config.dart	getDefaultBundledPath now also probes assets/windows/x86_64/<tool>.exe before assets/windows/<tool>.exe (matching the macOS/Linux behaviour)
gui/lib/patcher/xdelta_patcher.dart, xdelta_builder.dart	existence preflight only rejects absolute paths, so a bare tool name resolved via the OS PATH is no longer falsely reported missing

Dynamic version

File	Change
core/bin/openrom.dart	--version uses readAppVersion() instead of the hard-coded 'v3.0.0' fallback → fixes CoreBridge.getVersion() and the About screen
core/lib/src/version_reader.dart	also honours --dart-define=APP_VERSION (priority: define → VERSION next to exe → VERSION in CWD → unknown)
.github/workflows/Release.yml, flatpak/io.github.M5Devs.OpenROM.yml	bundle the VERSION file next to the core (and GUI) binaries so readAppVersion() finds it at runtime

Docs

• docs/DEVELOPER_ONBOARDING.md — architecture, IPC bridge, conversion pipeline, tool resolution, state management, and CI/CD packaging lifecycle.

Behaviour

# before
xdelta3 → <exeDir>/xdelta3.exe   (missing in packaged installs → patch fails)
--version → OpenROM v3.0.0        (hard-coded fallback)

# after
xdelta3 → assets/windows/x86_64/xdelta3.exe  (then assets/windows/, then PATH)
--version → OpenROM v<real version from bundled VERSION file>

Testing

• ⚠️ Not run in this environment — no Dart/Flutter toolchain is available here, so flutter analyze / dart test were not executed. Changes were verified by inspection and are type-safe (removed the now-unused dart:io import; added the path import where needed).
• Suggested verification: flutter analyze + flutter test in gui/, dart analyze + dart test in core/ (the quality.yml gate), and a manual xdelta patch on a Windows build.

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This PR was created by an AI agent (OpenHands) on behalf of the user.