Use native upgrade commands for Claude Code and Codex

[lilly-luo]

this PR does the following:

1/ use native upgrade cmd for cc + codex (claude update, codex upgrade) instead of going thru npm which doesnt respect our internal databricks proxy
2/ consolidate the upgrade logic
3/ prompt y/n from user for upgrade (instead of just doing it) for safety

testing:

cc - doesn't ask me to update unless i need it

$ claude --version
2.1.247 (Claude Code)
# lilly.luo at ip-10-93-35-82 in ~/worktrees/ucode-demo (git:lilly/fix-upgrade-cmds) [18:58:25]
$ uv run ucode claude
      Built ucode @ file:///home/lilly.luo/worktrees/ucode-demo
Uninstalled 1 package in 2ms
Installed 1 package in 1ms

╭──────────────────────────────────────────╮
│ Launching Claude Code with Unity Gateway │
╰──────────────────────────────────────────╯
✔ Starting Claude Code
# lilly.luo at ip-10-93-35-82 in ~/worktrees/ucode-demo (git:lilly/fix-upgrade-cmds) [18:58:33]
$ uv run ucode claude --enable-smart-routing
! Smart routing requires Claude Code 2.1.248 or newer. Your current version is Claude Code 2.1.247.
Upgrade Claude Code if available? (y/n) › y
• Upgrading Claude Code...
Current version: 2.1.247
Checking for updates to latest version...
Updating to 2.1.260...
Successfully updated from 2.1.247 to version 2.1.260
✔ Claude Code is up to date

╭──────────────────────────────────────────╮
│ Launching Claude Code with Unity Gateway │
╰──────────────────────────────────────────╯
✔ Starting Claude Code
• Smart routing v2: the first submitted prompt will select Claude Code's model; log: /home/lilly.luo/.ucode/claude-v2-pty.log.

codex -- doesn't ask me to update unless i need it

$ codex --version
codex-cli 0.152.1

$ uv run ucode codex 
# comes up 

$ uv run ucode codex --enable-smart-routing
! Codex smart routing requires Codex 0.145.0 or newer; found 0.143.0.
Upgrade Codex if available? (y/n) › y
# upgrades and comes up