Rewrite from Go + vanilla JS to Python (FastAPI) + React (TypeScript)

- Backend: Python 3.12 with FastAPI, SQLAlchemy, boto3
- Frontend: React 18 with TypeScript, Vite build tooling
- Updated Dockerfile for multi-stage Node + Python build
- Updated CI pipeline for Python backend
- Removed old Go code (cmd/, internal/, go.mod, go.sum)
- Updated README with new tech stack documentation

backend/app/storage.py

@@ -0,0 +1,83 @@
+import hashlib
+from typing import BinaryIO, Tuple
+import boto3
+from botocore.config import Config
+from botocore.exceptions import ClientError
+
+from .config import get_settings
+
+settings = get_settings()
+
+
+class S3Storage:
+    def __init__(self):
+        config = Config(s3={"addressing_style": "path"} if settings.s3_use_path_style else {})
+
+        self.client = boto3.client(
+            "s3",
+            endpoint_url=settings.s3_endpoint if settings.s3_endpoint else None,
+            region_name=settings.s3_region,
+            aws_access_key_id=settings.s3_access_key_id,
+            aws_secret_access_key=settings.s3_secret_access_key,
+            config=config,
+        )
+        self.bucket = settings.s3_bucket
+
+    def store(self, file: BinaryIO) -> Tuple[str, int]:
+        """
+        Store a file and return its SHA256 hash and size.
+        Content-addressable: if the file already exists, just return the hash.
+        """
+        # Read file and compute hash
+        content = file.read()
+        sha256_hash = hashlib.sha256(content).hexdigest()
+        size = len(content)
+
+        # Check if already exists
+        s3_key = f"fruits/{sha256_hash[:2]}/{sha256_hash[2:4]}/{sha256_hash}"
+
+        if not self._exists(s3_key):
+            self.client.put_object(
+                Bucket=self.bucket,
+                Key=s3_key,
+                Body=content,
+            )
+
+        return sha256_hash, size, s3_key
+
+    def get(self, s3_key: str) -> bytes:
+        """Retrieve a file by its S3 key"""
+        response = self.client.get_object(Bucket=self.bucket, Key=s3_key)
+        return response["Body"].read()
+
+    def get_stream(self, s3_key: str):
+        """Get a streaming response for a file"""
+        response = self.client.get_object(Bucket=self.bucket, Key=s3_key)
+        return response["Body"]
+
+    def _exists(self, s3_key: str) -> bool:
+        """Check if an object exists"""
+        try:
+            self.client.head_object(Bucket=self.bucket, Key=s3_key)
+            return True
+        except ClientError:
+            return False
+
+    def delete(self, s3_key: str) -> bool:
+        """Delete an object"""
+        try:
+            self.client.delete_object(Bucket=self.bucket, Key=s3_key)
+            return True
+        except ClientError:
+            return False
+
+
+# Singleton instance
+_storage = None
+
+
+def get_storage() -> S3Storage:
+    global _storage
+    if _storage is None:
+        _storage = S3Storage()
+    return _storage