Rewrite app: entries → projects with S3 file storage

Replace flat text entries with project-based structure.
Each project has name, local/corp fields, content textarea,
and file upload (up to 100MB) stored in MinIO S3.
New API: CRUD projects + file download + content copy.
Frontend: two views (project list + project page).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/Cargo.toml

@@ -4,10 +4,12 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
-axum = "0.8"
+axum = { version = "0.8", features = ["multipart"] }
 sqlx = { version = "0.8", features = ["runtime-tokio", "postgres", "chrono"] }
 tokio = { version = "1", features = ["full"] }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 tower-http = { version = "0.6", features = ["cors"] }
 chrono = { version = "0.4", features = ["serde"] }
+rust-s3 = "0.35"
+uuid = { version = "1", features = ["v4"] }