🎨 Polish: Improve button feedback and touch targets

[yuga-hashimoto]

🎨 Polish: Improve button feedback and touch targets

💡 What

This PR makes two highly targeted UX improvements:

1. Loading State Feedback: Added a CircularProgressIndicator alongside the "Connecting..." text in the main connection button.
2. Accessibility Compliance: Removed hardcoded Modifier.size(24.dp) restrictions on several IconButton components across MainActivity and ChatActivity.

🎯 Why

• Loading State: Previously, the connection button only changed its text to "Connecting...", which lacked clear, active visual feedback that an operation was in progress. The spinner makes the loading state much more explicit.
• Accessibility: Android accessibility guidelines strongly recommend a minimum touch target size of 48x48dp for interactive elements. By explicitly sizing the IconButton to 24dp, the application was violating this guideline, making the buttons harder to reliably tap, especially for users with motor impairments. Removing the modifier allows the IconButton to size itself appropriately to meet these standards.

📸 Before/After

• Before: Connection button just said "Connecting...". Several icon buttons were exactly 24x24dp.
• After: Connection button shows a white spinner + "Connecting...". Icon buttons now have standard accessible padding while keeping the inner icon at an appropriate visual size.

♿ Accessibility

This change directly resolves multiple accessibility touch target violations by allowing standard Compose IconButton behavior to enforce the 48dp minimum touch boundary.

🔬 Verification

• Tested locally by modifying MainActivity.kt and ChatActivity.kt.
• Compiled successfully with ./gradlew app:assembleStandardDebug and ran full unit test suite app:testStandardDebugUnitTest with no regressions.
• Code review passed.

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PR created automatically by Jules for task 11883682284153437201 started by @yuga-hashimoto

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