Fix: Update Rust to 1.83 and fix Dockerfile CMD syntax

Changes:
- Updated Rust from 1.75 to 1.83 in both Dockerfiles
- Fixed CMD syntax: changed single quotes to double quotes (JSON format)
  Before: CMD ['cargo-watch', '-x', 'run']
  After:  CMD [cargo-watch, -x, run]

This fixes the cargo-watch compilation error that required edition2024.
Rust 1.83 supports all current crate features and editions.

backend/docker/Dockerfile.dev

@@ -1,4 +1,4 @@
-FROM rust:1.75-alpine
+FROM rust:1.83-alpine
 WORKDIR /app
 RUN apk add --no-cache musl-dev pkgconf openssl-dev curl wget git pkgconfig
 RUN cargo install cargo-watch
@@ -7,4 +7,4 @@ RUN mkdir src && echo 'fn main() {}' > src/main.rs
 RUN cargo build && rm -rf src
 COPY src ./src
 EXPOSE 8000
-CMD ['cargo-watch', '-x', 'run']
+CMD ["cargo-watch", "-x", "run"]