feat: eagerly move credetials to depot, allow args to julia on jh run

[pankgeorg]

Improve Julia credentials management and jh run command

This PR enhances the Julia integration with automatic credential management and a more
intuitive command structure.

Changes

Automatic Julia Credentials Management

• Julia credentials (~/.julia/servers//auth.toml) are now automatically
  created/updated when:
  • Running jh auth login
  • Running jh auth refresh
  • Running jh run or jh run setup
  • Tokens are automatically refreshed via ensureValidToken()
• Credentials use atomic file writes (temp file + rename) to prevent corruption

New Command Structure

• jh run [-- julia-args...] - Runs Julia with JuliaHub configuration (previously only
  setup credentials)
  • Sets up credentials automatically before starting Julia
  • Arguments after -- are passed directly to Julia
  • Environment variables configured: JULIA_PKG_SERVER, JULIA_PKG_USE_CLI_GIT
• jh run setup - New subcommand for credentials-only setup without starting Julia

Implementation

• Extracted setupJuliaCredentials() as a reusable function called by:
  • jh run command (before starting Julia)
  • jh run setup command
  • jh auth login command (after successful login)
  • jh auth refresh command (after successful refresh)
• Added updateJuliaCredentialsIfNeeded() function that automatically updates credentials
  during token refresh

Documentation

• Updated CLAUDE.md with comprehensive Julia integration details
• Updated README.md with Julia workflow examples
• Updated command help text with correct usage patterns

Examples

  # Setup credentials only
  jh run setup

  # Start Julia REPL
  jh run

  # Run a Julia script
  jh run -- script.jl

  # Execute Julia code
  jh run -- -e "println(\"Hello from JuliaHub!\")"

  # Run with project and threads
  jh run -- --project=. --threads=4 script.jl