feat(leaderboard): add ETag/304 caching on /api/leaderboard

[Obaara293]

Overview

This PR adds strong ETag support to both /api/leaderboard endpoints (GET / and GET /user/:stellarAddress) to enable conditional GET responses — cutting bandwidth on repeat reads via 304 Not Modified.

Related Issue

Closes #635

Changes

Routes

• [MODIFY] src/routes/leaderboard.ts — added conditionalGet to GET / and GET /user/:stellarAddress:
  • Every 200 response now includes ETag (SHA-256 of the JSON payload) and Cache-Control: no-cache headers
  • When the client sends If-None-Match matching the current ETag, responds with 304 Not Modified (no body)
  • Bare-hash (unquoted) If-None-Match values are handled correctly via existing middleware normalization

Tests

• [ADD] src/__tests__/routes/leaderboard.test.ts — 10 new integration tests covering:
  • ETag and Cache-Control headers on first request
  • 304 when If-None-Match matches
  • 200 when ETag is stale
  • 304 with unquoted (bare hash) If-None-Match
  • ETag stability across identical payloads
  • ETag changes when payload changes
  • 304 response includes ETag header
  • Same coverage for the user-specific endpoint

Config

• [MODIFY] jest.config.js — added src/__tests__/**/*.test.ts to test match pattern so co-located tests are discovered

Verification Results

npm test -- src/__tests__/routes/leaderboard.test.ts -t "ETag"
✅ 10/10 passed

PASS src/__tests__/routes/leaderboard.test.ts (19.6s)
  Leaderboard Routes
    ETag / 304 conditional GET for GET /api/leaderboard
      ✓ returns 200 with ETag and Cache-Control on first request
      ✓ returns 304 when If-None-Match matches current ETag
      ✓ returns 200 when If-None-Match does not match
      ✓ returns 304 with unquoted (bare hash) If-None-Match
      ✓ ETag is stable across repeated requests for the same data
      ✓ ETag changes when leaderboard data changes
      ✓ 304 still includes ETag header
    ETag / 304 conditional GET for GET /api/leaderboard/user/:stellarAddress
      ✓ returns 200 with ETag and Cache-Control on first request
      ✓ returns 304 when If-None-Match matches
      ✓ returns 200 when If-None-Match does not match

Acceptance Criteria	Status
ETag emitted on GET /api/leaderboard	✅ Strong ETag via SHA-256 hash of JSON payload
ETag emitted on GET /api/leaderboard/user/:stellarAddress	✅ Strong ETag via SHA-256 hash of JSON payload
304 returned when If-None-Match matches	✅ Both endpoints return 304 with no body
Cache-Control: no-cache on every response	✅ Clients may cache but must revalidate
Deterministic ETags (sorted keys)	✅ Uses sortedReplacer from existing etag.ts middleware
10 focused tests added	✅ All pass

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[greatest0fallt1me]

Green across the board — merging. Thanks!