Centralize response cache policy

[BradNut]

Summary

• add a server-only response cache module for cached JSON reads/writes and cache-control TTL policy
• move Articles and Bandcamp album endpoints behind the shared cache interface
• cover cache hit, TTL fallback, miss, disabled cache, Redis unavailable, and write expiry behavior

Validation

• SENTRY_AUTH_TOKEN=test BANDCAMP_USERNAME=test WALLABAG_CLIENT_ID=test WALLABAG_CLIENT_SECRET=test WALLABAG_USERNAME=test WALLABAG_PASSWORD=test pnpm check
• SENTRY_AUTH_TOKEN=test BANDCAMP_USERNAME=test WALLABAG_CLIENT_ID=test WALLABAG_CLIENT_SECRET=test WALLABAG_USERNAME=test WALLABAG_PASSWORD=test pnpm test:unit run
• pnpm biome lint src/lib/server/responseCache.ts src/lib/server/responseCache.test.ts src/lib/services/articlesApi.ts src/routes/api/bandcamp/albums/+server.ts

Closes #60

[github-actions]

🌿 Fallow

✅ No code issues · ✅ No duplication · ⚠️ 5 health findings

See inline review comments for per-finding details.

Complexity (5 functions above threshold)

File	Function	Severity	Cyclomatic	Cognitive	CRAP	Lines
bandcamp/albums/+server.ts:8	GET	high	7	5	56.0 !	45
lib/server/responseCache.ts:57	readCachedJson	moderate	6	5	42.0 !	36
lib/services/articlesApi.ts:100	<arrow>	moderate	5	4	30.0 !	18
lib/services/articlesApi.ts:131	fetchArticlesApi	moderate	5	3	30.0 !	29
lib/services/articlesApi.ts:120	buildFallbackResponse	moderate	5	2	30.0 !	10

4 files, 19 functions analyzed (thresholds: cyclomatic > 20, cognitive > 15, CRAP >= 30.0)

Codebase health

Metric	Value
Maintainability	91.5 / 100
Avg complexity	3

Issue counts scoped to files changed since 4a755ef · health metrics reflect the full codebase

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud