perf: add idempotent MongoDB index-creation script

[xpoes123]

The application defines no MongoDB indexes, so several hot query paths fall back to full collection scans. This adds an idempotent operator script (database/create-indexes.js, invoked via npm run create-indexes) that ensures the indexes the existing queries already filter and sort on.

Background

Query paths such as get-query, get-random-tossups, get-packet, and the leaderboard/user-stats aggregations operate against collections with no supporting indexes. The script reuses the existing collection handles from database/qbreader/collections.js and database/account-info/collections.js — no second client or connection is opened.

Changes

• database/create-indexes.js — new idempotent script; calls createIndex for each entry in a documented table and logs the confirmed index name per call. createIndex is a no-op when an equivalent index already exists.
• package.json — adds "create-indexes": "node database/create-indexes.js" script.

Indexes created and the queries they serve:

qbreader.tossups / qbreader.bonuses

• { 'set.name': -1, 'packet.number': 1, number: 1 } — get-query result sort; get-set and get-pg-lookup filters and sorts.
• { 'set.year': 1 } — year-range $match in get-random-tossups / get-random-bonuses, get-frequency-list, and get-query year filters.
• { 'packet._id': 1, number: 1 } — get-packet (filter by packet._id, sort by number) and the packet-metadata-list $lookup.

qbreader.packets

• { 'set.name': 1, number: 1 } — get-packet findOne, get-num-packets countDocuments, get-packet-list find.
• { 'set._id': 1 } — packet-metadata-list $match.

qbreader.sets

• { name: 1 } — get-set-id and rename-set findOne({ name }).

account-info.tossup-stars / account-info.bonus-stars

• { user_id: 1 } — every star operation (get-ids, is-starred, star, unstar, clear) filters on user_id.

account-info.per-tossup-data / account-info.per-bonus-data

• { 'data.user_id': 1 } — leaderboard grouping and user-stats match.
• { set_id: 1 } — user-stats set filter.

Risk & testing

This is purely additive: a btree index never changes query results, it only speeds up filters and sorts. The unanchored $regex substring search is unaffected. createIndex is idempotent and modern MongoDB builds indexes non-blocking, so the script is safe to re-run. Verified with node --check and semistandard.

The script has not been run against the database in this PR. An operator must execute npm run create-indexes against the production database after merging.