Fix 975 via "No history requests" message

[Aman071106]

PR Description

Adds a clear "No history requests" empty state to the History tab. Previously, it showed a blank screen which looked like a loading error.

Changes:

• Modified HistoryPane to check if sortedHistoryKeys is empty.
• Returns a Centered Placeholder (Icon + Text) using theme colors when no history exists.
• Keeps existing behavior when functionality is populated.

Related Issues

• Closes Empty History state renders blank UI with no table or placeholder #975

Checklist

• I have gone through the contributing guide
• I have updated my branch and synced it with project main branch before making this PR
• I am using the latest Flutter stable branch
• I have verified the fix manually

Added/updated tests?

• No, and this is why: UI state change verified visually.

OS on which you have developed and tested the feature?

• Windows

Reference Images

Before (Windows)

After (Windows)

Before (Mobile)

After (Mobile)