Prepare build-time static asset syncing without touching page templates

Constraint: Static images need to come from remote sources before log sync and build
Rejected: Per-file source mapping | directory-grouped manifests are easier to maintain
Confidence: high
Scope-risk: narrow
Directive: Prefer grouped target_dir manifests and keep page-facing paths stable
Tested: npm run assets:sync; npm run build; bash -n scripts/deploy-homepage.sh; npx tsc --noEmit --pretty false --project tsconfig.json
Not-tested: Real Seafile download against production URLs

src/content/static-assets/index.json

@@ -0,0 +1,24 @@
+[
+  {
+    "target_dir": "public/images/projects",
+    "files": []
+  },
+  {
+    "target_dir": "public/images/gallery",
+    "files": 
+    [
+	{
+	    "url": "http://106.12.111.150:8000/f/0d357852716f492eb92f/?dl=1",
+	    "filename": "Alphys.png"
+	},
+	{
+	    "url": "http://106.12.111.150:8000/f/ec2e2e282ed7478c8fa0/?dl=1",
+	    "filename": "Asgore.png"
+	},
+	{
+	    "url": "http://106.12.111.150:8000/f/7b7fb8414ab2485ba05a/?dl=1",
+	    "filename": "Asriel.png"
+	}
+    ]
+  }
+]