Add backend API for projects & snapshots

Introduce full backend API surface for projects, snapshots and user pubkeys: controllers, DTOs, JPA entities, repositories, services, and tests. Add SecurityConfig improvements (JWT decoder, audience/issuer/timestamp validation and CORS), a GlobalExceptionHandler for consistent error responses, and remove a stray test call from BackendApplication. Also update README (architecture, docs, CLI/Frontend/Backend notes), add CLAUDE.md, VSCode settings, and multiple frontend/CLI Rust changes. Small housekeeping: add .DS_Store and test adjustments.

cli/envsync-cli/Cargo.toml

@@ -5,7 +5,9 @@ edition = "2024"
 
 [dependencies]
 anyhow = "1.0.102"
-clap = "4.5.60"
+clap = { version = "4.5.60", features = ["derive", "env"] }
+argon2 = "0.5"
+base64 = "0.22"
 comfy-table = "7.2.2"
 console = "0.16.2"
 ctrlc = "3.5.2"