feat: complete dashboard onboarding walkthrough

[Roopathanushree]

Summary

Adds an interactive onboarding walkthrough for first-time DevTrack dashboard users. The tour explains important widgets, remembers completion, supports skipping, and can be replayed from the dashboard header.

Closes #2438

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Type of Change

• 🐛 Bug fix
• ✨ New feature
• 💥 Breaking change
• 📝 Documentation update
• ♻️ Refactor / code cleanup
• ⚡ Performance improvement
• 🔒 Security fix
• 🧪 Tests only

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• ✨ New feature
• Linked the related issue above
• Self-reviewed my own diff
• No unnecessary console logs, debug code, or commented-out blocks
• pnpm lint passes locally
• No TypeScript errors (pnpm type-check)
• ARIA labels/roles added where needed

What Changed

• Added a six-step Driver.js onboarding walkthrough
• Added stable tour target IDs to dashboard widgets
• Added automatic first-time launch and completion persistence
• Added Next, Back, Skip Tour, and progress controls
• Added a Replay Tour button to the dashboard header
• Added a final CTA directing users to the goal tracker
• Safely skips unavailable or hidden dashboard widgets

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How to Test

1. Sign in and open the dashboard.

2. Run this in the browser console:

   localStorage.removeItem("devtrack-dashboard-onboarding-completed");
   location.reload();

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[github-actions]

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