[FEATURE] Add placeholder with example repository suggestions

[ascender1729]

Description

Show example repository suggestions in the search input placeholder or as quick-select chips.

Why Needed

• Helps new users understand expected input format
• Provides quick access to popular repos
• Improves discoverability

Implementation Details

• Add placeholder text like 'Try: facebook/react, microsoft/vscode'
• Optionally add clickable chips below input
• Rotate suggestions or show random popular repos

Example Repos to Suggest

• facebook/react
• microsoft/vscode
• vercel/next.js
• sveltejs/svelte
• astro/astro

Files to Modify

• src/components/results/ResultsContainer.svelte
• src/lib/constants.ts (for repo list)

Acceptance Criteria

• Placeholder shows example format
• Optional: clickable repo chips
• Clicking chip fills input with repo
• Mobile-friendly display

Time Estimates

• With AI: 90 minutes
• Without AI: 600 minutes