add user interest-based recommendation engine with onboarding

[RayanBatada]

Adds a recommendation engine that personalizes the posts feed based on user interests. New users are shown an onboarding modal to select their interests on first login.

Schema

• schema/tables.ts: Added userInterests table with weighted tag preferences
• schema/tables.ts: Added onboardingCompleted field to users table

Components

• components/OnboardingModel/index.tsx: New modal for interest selection with DevDogs logo
• components/OnboardingModel/OnboardingWrapper.tsx: Wrapper to conditionally show modal

Server Actions

• server/actions/interests.ts: Actions for saving/skipping onboarding and updating interest weights

Recommendation Engine

• lib/recommendations/constants.ts: Weight constants for interest scoring
• lib/recommendations/getRecommendedPosts.ts: Query that sorts posts by user interest match

Other

• app/layout.tsx: Check onboarding status and render modal wrapper
• tags.json: Expanded interest categories (Career, Involvement, Academics, Technology)

1. New users see onboarding modal on first visit
2. Users select interests (tags) they care about
3. Interests are saved with initial weight of 2.0
4. Posts are sorted by relevance score (sum of matching interest weights)
5. Posts matching user interests appear first in the feed