Vendor backend and frontend into the monorepo

The submodule collapse was only half applied: .gitmodules was deleted but
backend/ and frontend/ were still recorded as gitlinks, so none of their
files were tracked. Replace the gitlinks with the real trees.

Also untrack .env (it carried placeholder secrets) in favour of a tracked
.env.example, drop the committed __pycache__, and narrow the blanket *.png
ignore that would have swallowed design assets.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

backend/app/main.py

@@ -0,0 +1,33 @@
+import sentry_sdk
+from fastapi import FastAPI
+from fastapi.routing import APIRoute
+from starlette.middleware.cors import CORSMiddleware
+
+from app.api.main import api_router
+from app.core.config import settings
+
+
+def custom_generate_unique_id(route: APIRoute) -> str:
+    return f"{route.tags[0]}-{route.name}"
+
+
+if settings.SENTRY_DSN and settings.ENVIRONMENT != "local":
+    sentry_sdk.init(dsn=str(settings.SENTRY_DSN), enable_tracing=True)
+
+app = FastAPI(
+    title=settings.PROJECT_NAME,
+    openapi_url=f"{settings.API_V1_STR}/openapi.json",
+    generate_unique_id_function=custom_generate_unique_id,
+)
+
+# Set all CORS enabled origins
+if settings.all_cors_origins:
+    app.add_middleware(
+        CORSMiddleware,
+        allow_origins=settings.all_cors_origins,
+        allow_credentials=True,
+        allow_methods=["*"],
+        allow_headers=["*"],
+    )
+
+app.include_router(api_router, prefix=settings.API_V1_STR)