fix: prevent NoSuchElementException in session chain selection

[developerfred]

close #211

• Replace first() with firstOrNull() in getSelectedChain extension function
• Add null safety check in onSessionApproved to handle empty chains case
• This resolves crash when AppKit.chains list is empty during session approval

[github-actions]

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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[developerfred]

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[developerfred]

recheck