Add campaign-scoped favorites for jurors

[Oyelakin-Mercy]

Fixes #333

Some Jurors have vote a lot of pictures, and scrolling through so many to see their favorite is stressful. This PR adds a "View Favorites" button to the juror campaign card, which allows them to quickly go to to their favorited images for a specific campaign.

Changes:

Frontend

• JurorCampaignCard.vue: Added a "View Favorites" button with a heart icon that navigates to the new faves view for the campaign
• VoteRating.vue, VoteYesNo.vue, VoteRanking.vue: Added a "View Favorites" button alongside the existing "Edit previous votes" button in both the active voting view and the all-done state
• router/index.js: Added new /vote/:id/faves route pointing to FavesView
• jurorService.js: Updated getFaves to accept campaignId and offset parameters
• en.json: Added montage-my-campaign-faves i18n string ("View Favorites")

Backend

• juror_endpoints.py: Updated get_faves endpoint to accept and pass campaign_id filter
• rdb.py:
  • JurorDAO.get_faves: Added campaign_id filter and fixed a bug where offset was hardcoded to 0
  • JurorDAO.fave: Fetch round_entry before checking for existing fave so campaign_id is available for scoping; fixes potential cross-campaign fave collisions
  • JurorDAO.unfave: Scoped unfave lookup by campaign_id and status; changed .one() to .one_or_none() to handle gracefully if fave doesn't exist
  • Vote.check_fave: Added campaign_id lookup so fave checks are scoped to the correct campaign