feat: Implement brand-aware release creation for Agravity

- Added support for multiple brands in release scripts, allowing for branded artifacts.
- Introduced brand configuration management with JSON files for each brand.
- Created a new `brand_config.py` script to handle brand-specific logic and asset resolution.
- Updated `create_release.ps1` and `create_release.sh` scripts to utilize brand configurations and generate release manifests.
- Added unit tests for brand configuration loading and release manifest generation.
- Introduced `agravity` brand with its specific configuration in `agravity.json`.

tests/unit/test_brand_config.py

@@ -0,0 +1,77 @@
+"""Tests for brand-aware build configuration helpers."""
+
+import json
+import sys
+from pathlib import Path
+
+BUILD_SCRIPTS_DIR = Path(__file__).resolve().parents[2] / "build" / "scripts"
+if str(BUILD_SCRIPTS_DIR) not in sys.path:
+    sys.path.insert(0, str(BUILD_SCRIPTS_DIR))
+
+from brand_config import generate_release_manifest, load_brand_config
+
+
+def test_load_agravity_brand_config():
+    """Test loading the Agravity brand manifest."""
+    brand = load_brand_config("agravity")
+
+    assert brand.brand_id == "agravity"
+    assert brand.display_name == "Agravity Bridge"
+    assert brand.asset_prefix == "AgravityBridge"
+    assert brand.exe_name == "AgravityBridge"
+    assert brand.windows_installer_name("0.8.4") == "AgravityBridge-0.8.4-win-x64.msi"
+
+
+def test_generate_release_manifest_for_agravity(tmp_path):
+    """Test generating a shared release manifest from local artifacts."""
+    project_root = tmp_path
+    (project_root / "build" / "brands").mkdir(parents=True)
+    (project_root / "build" / "dist" / "windows" / "agravity").mkdir(parents=True)
+    (project_root / "build" / "dist" / "macos" / "agravity").mkdir(parents=True)
+
+    source_manifest = Path(__file__).resolve().parents[2] / "build" / "brands" / "agravity.json"
+    (project_root / "build" / "brands" / "agravity.json").write_text(
+        source_manifest.read_text(encoding="utf-8"),
+        encoding="utf-8",
+    )
+
+    win_installer = (
+        project_root
+        / "build"
+        / "dist"
+        / "windows"
+        / "agravity"
+        / "AgravityBridge-0.8.4-win-x64.msi"
+    )
+    win_installer.write_bytes(b"msi")
+    (win_installer.parent / f"{win_installer.name}.sha256").write_text("abc", encoding="utf-8")
+
+    mac_installer = (
+        project_root
+        / "build"
+        / "dist"
+        / "macos"
+        / "agravity"
+        / "AgravityBridge-0.8.4-macos-universal.dmg"
+    )
+    mac_installer.write_bytes(b"dmg")
+    (mac_installer.parent / f"{mac_installer.name}.sha256").write_text("def", encoding="utf-8")
+
+    output_path = project_root / "build" / "dist" / "release-manifest.json"
+    generate_release_manifest(
+        "0.8.4",
+        ["agravity"],
+        output_path=output_path,
+        root=project_root,
+    )
+
+    manifest = json.loads(output_path.read_text(encoding="utf-8"))
+    assert manifest["version"] == "0.8.4"
+    assert (
+        manifest["brands"]["agravity"]["windows-x64"]["installer"]
+        == "AgravityBridge-0.8.4-win-x64.msi"
+    )
+    assert (
+        manifest["brands"]["agravity"]["macos-universal"]["installer"]
+        == "AgravityBridge-0.8.4-macos-universal.dmg"
+    )