🎨 Polish: Improve connection loading state UX

[yuga-hashimoto]

💡 What: Added an inline CircularProgressIndicator to the SystemStatusCard in MainActivity.kt that is visible exclusively when the gateway connection is in an active "Connecting" state.

🎯 Why: Previously, the connection status relied entirely on text ("Connecting...") and color changes, which lacked an active indication that a background process was ongoing. Adding a subtle spinner improves the loading/retry state feedback and connection status clarity without disrupting the existing design language.

📸 Before/After:

• Before: Text simply says "Connecting..." with a static dot.
• After: Text says "Connecting..." alongside an actively spinning loading indicator, providing clear visual reinforcement of the loading state.

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PR created automatically by Jules for task 5503882210065059956 started by @yuga-hashimoto

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