chore(mpc-system): update Dockerfiles to Go 1.24 and fix line endings

- Update all Dockerfiles from Go 1.21 to Go 1.24 (required by go.mod)
- Fix line endings in deploy.sh and .env.example for Unix compatibility

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/mpc-system/services/account/Dockerfile

@@ -1,5 +1,5 @@
 # Build stage
-FROM golang:1.21-alpine AS builder
+FROM golang:1.24-alpine AS builder
 
 RUN apk add --no-cache git ca-certificates
 

backend/mpc-system/services/message-router/Dockerfile

@@ -1,5 +1,5 @@
 # Build stage
-FROM golang:1.21-alpine AS builder
+FROM golang:1.24-alpine AS builder
 
 RUN apk add --no-cache git ca-certificates
 

backend/mpc-system/services/server-party-api/Dockerfile

@@ -1,5 +1,5 @@
 # Build stage
-FROM golang:1.21-alpine AS builder
+FROM golang:1.24-alpine AS builder
 
 RUN apk add --no-cache git ca-certificates
 

backend/mpc-system/services/server-party/Dockerfile

@@ -1,5 +1,5 @@
 # Build stage
-FROM golang:1.21-alpine AS builder
+FROM golang:1.24-alpine AS builder
 
 RUN apk add --no-cache git ca-certificates
 

backend/mpc-system/services/session-coordinator/Dockerfile

@@ -1,5 +1,5 @@
 # Build stage
-FROM golang:1.21-alpine AS builder
+FROM golang:1.24-alpine AS builder
 
 # Install dependencies
 RUN apk add --no-cache git ca-certificates