[FEATURE] Add keyboard shortcut hint for Enter key

[ascender1729]

Description

Show a visual hint near the search input indicating that pressing Enter submits the search.

Why Needed

• Not all users know Enter triggers search
• Improves discoverability
• Professional UX touch

Implementation Details

• Add small 'Press Enter' or keyboard icon hint
• Position near search button or inside input
• Use subtle styling (doesn't distract)
• Hide on mobile where less relevant

Files to Modify

• src/components/results/ResultsContainer.svelte

Design Options

1. Text hint: 'Press Enter to search'
2. Keyboard icon with 'Enter' label
3. Integrated into input placeholder

Acceptance Criteria

• Hint visible near search input
• Subtle, non-intrusive styling
• Hidden on small screens (optional)
• Accessible to screen readers

Time Estimates

• With AI: 150 minutes
• Without AI: 990 minutes