Show semantic search UI when available and evict old Redis indexes

[vaclisinc]

Overview

This PR limits when the semantic search UI is shown and introduces eviction for Redis indexes to prevent memory issues.

Problem Statement

Frontend Logic

• The semantic search UI is currently shown for every semester.
• Clicking into the UI triggers index building.
• This leads to excessive Redis memory usage and can cause OOM due to too many indexes being created and retained.

Refresh Logic

• Old Redis indexes were not being cleaned up, causing stale or incorrect search results and unnecessary memory usage.

Solution

• Only show the semantic search UI when it is actually available, instead of for all semesters.
• Add eviction logic to remove old Redis indexes and control memory usage.

[github-actions]

Linting Failed

Note: The status check will always pass. Run npm run lint -- --continue to see the full output locally.

Click to expand lint output

> lint
> turbo run lint --continue --output-logs=errors-only


Attention:
Turborepo now collects completely anonymous telemetry regarding usage.
This information is used to shape the Turborepo roadmap and prioritize features.
You can learn more, including how to opt-out if you'd not like to participate in this anonymous program, by visiting the following URL:
https://turborepo.com/docs/telemetry

• Packages in scope: @repo/BtLL, @repo/common, @repo/eslint-config, @repo/gql-typedefs, @repo/shared, @repo/sis-api, @repo/storybook, @repo/theme, @repo/typescript-config, ag-frontend, api-sandbox, backend, datapuller, frontend, staff-frontend
• Running lint in 15 packages
• Remote caching disabled
�[;31mbackend:lint�[;0m
cache miss, executing d3bf246a0280e657

> lint
> eslint src/


/home/runner/work/berkeleytime/berkeleytime/apps/backend/src/modules/semantic-search/client.ts
  50:13  error  Empty block statement  no-empty

✖ 1 problem (1 error, 0 warnings)

npm error Lifecycle script `lint` failed with error:
npm error code 1
npm error path /home/runner/work/berkeleytime/berkeleytime/apps/backend
npm error workspace backend
npm error location /home/runner/work/berkeleytime/berkeleytime/apps/backend
npm error command failed
npm error command sh -c eslint src/
[WARN] command finished with error, but continuing...
::error::backend#lint: command (/home/runner/work/berkeleytime/berkeleytime/apps/backend) /opt/hostedtoolcache/node/22.12.0/x64/bin/npm run lint exited (1)

 Tasks:    6 successful, 7 total
Cached:    0 cached, 7 total
  Time:    11.593s 
Failed:    backend#lint

 ERROR  run failed: command  exited (1)

[johngerving]

LGTM