[FEATURE] Bookmark/save issues for later #67

Feature Description

Add a bookmark/save feature that allows users to save interesting GitHub issues for later review. Users can mark issues as "saved" from the match/search pages and access them from a dedicated "Saved Issues" section in their profile.

Problem Statement

Currently, when users browse through matched issues, they have no way to save issues they find interesting but aren't ready to work on immediately. Users must either start working on an issue right away or lose track of it. This creates friction in the contribution workflow and may cause users to miss good opportunities.

Proposed Solution

Frontend:

• Add a bookmark icon (star/bookmark) to each issue card on match and search pages
• Create a new "Saved Issues" tab in the profile page
• Show saved count badge on profile navigation
• Allow users to unsave issues with a single click

Backend:

• Add saved_issues array field to user document in Firebase
• Create API endpoints:
  • POST /api/v1/issues/save - Save an issue
  • DELETE /api/v1/issues/save/{issue_id} - Unsave an issue
  • GET /api/v1/issues/saved - Get all saved issues
• Store issue metadata (title, repo, URL, labels) to avoid re-fetching

User Flow:

1. User clicks bookmark icon on issue card
2. Issue is saved to their profile in Firebase
3. User can view all saved issues in profile → Saved Issues tab
4. User can click to open issue on GitHub or unsave it

Component

Frontend

Alternative Solutions

No response

Additional Context

Similar implementations:

• GitHub's "Save for later" feature on discussions
• LinkedIn's "Save post" functionality
• Reddit's saved posts feature
• UI Mockup idea:

Bookmark icon in top-right corner of issue cards

• Filled star = saved, outline star = not saved
• Toast notification: "Issue saved!" / "Issue removed from saved"
• Saved Issues tab shows cards in same format as match page