Address CodeRabbit review feedback

- Fix null-safe operator on currentTeam() call in Upgrade.php
- Add --rm flag to docker run in upgrade.sh for cleanup consistency
- Store beforeunload handler as named reference and clean up on success
- Add clarifying comments for upgrade method calls
- Add error state handling with close option in upgrade modal
- Add step mapping documentation comment in upgrade-progress component

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/Livewire/Upgrade.php

@@ -55,7 +55,7 @@ class Upgrade extends Component
     public function getUpgradeStatus(): array
     {
         // Only root team members can view upgrade status
-        if (auth()->user()?->currentTeam()->id !== 0) {
+        if (auth()->user()?->currentTeam()?->id !== 0) {
             return ['status' => 'none'];
         }