Fix rating aggregation: use video_ratings counter table instead of writing to videos

[pmcfadin]

Problem

_update_video_aggregate_rating() in app/services/rating_service.py (lines 31-71) tries to $set three camelCase columns on the videos table that don't exist in the Cassandra schema:

• averageRating
• totalRatingsCount
• updatedAt

This produces an UNKNOWN_TABLE_COLUMNS error on every rating submission:

WARNING:astrapy.utils.api_commander:APICommander about to raise from: 
[{'errorCode': 'UNKNOWN_TABLE_COLUMNS', 'message': 'The table killrvideo.videos defines the columns: 
videoid, added_date, ... views, youtube_id. The update included the following unknown columns: 
"averageRating", "totalRatingsCount", "updatedAt".'}]

The error is silently caught (lines 64-71), so ratings return 200 — but aggregated values are never persisted, and get_video_ratings_summary() always returns averageRating=None, totalRatingsCount=0.

Root Cause

The schema has a dedicated counter table for this purpose that isn't being used:

CREATE TABLE IF NOT EXISTS killrvideo.video_ratings (
    videoid uuid PRIMARY KEY,
    rating_counter counter,
    rating_total counter
);

Required Changes

Write path (_update_video_aggregate_rating)

Replace the $set on videos with counter operations on video_ratings:

• On new rating: increment rating_counter by 1, increment rating_total by the rating value
• On updated rating: increment rating_total by (new_rating - old_rating) (counter stays the same)
• Note: Counters use $inc, not $set

Read path (get_video_ratings_summary)

Instead of reading averageRating/totalRatingsCount from the Video model (which are always None/0):

1. Query the video_ratings table for the video's rating_counter and rating_total
2. Compute average = rating_total / rating_counter on the fly
3. Return the computed values

Files to modify

• app/services/rating_service.py — rewrite _update_video_aggregate_rating() and get_video_ratings_summary()
• app/models/video.py — consider removing averageRating, totalRatingsCount, updatedAt fields (or keeping them as API-only computed fields)
• tests/services/test_rating_service.py — update tests for the new approach

Acceptance criteria

• Rating submission uses video_ratings counter table (not videos)
• GET /videos/{id}/ratings returns correct averageRating and totalRatingsCount
• No more UNKNOWN_TABLE_COLUMNS warnings in logs
• Existing tests pass, new tests cover counter logic