fix: correct test imports and health endpoint assertions

- Fix import in test_db_utils.py: use app.models instead of backend.app.models
- Update health endpoint test to expect 'ok' status and infrastructure keys
- Add CHANGELOG entries for PyPI proxy performance improvements

CHANGELOG.md

@@ -7,6 +7,23 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 ### Added
+- Added HTTP connection pooling infrastructure for improved PyPI proxy performance
+  - `HttpClientManager` with configurable pool size, timeouts, and thread pool executor
+  - Eliminates per-request connection overhead (~100-500ms → ~5ms)
+- Added Redis caching layer with category-aware TTL for hermetic builds
+  - `CacheService` with graceful fallback when Redis unavailable
+  - Immutable data (artifact metadata, dependencies) cached forever
+  - Mutable data (package index, versions) uses configurable TTL
+- Added `ArtifactRepository` for batch database operations
+  - `batch_upsert_dependencies()` reduces N+1 queries to single INSERT
+  - `get_or_create_artifact()` uses atomic ON CONFLICT upsert
+- Added infrastructure status to health endpoint (`/health`)
+  - Reports HTTP pool size and worker threads
+  - Reports Redis cache connection status
+- Added new configuration settings for HTTP client, Redis, and cache TTL
+  - `ORCHARD_HTTP_MAX_CONNECTIONS`, `ORCHARD_HTTP_CONNECT_TIMEOUT`, etc.
+  - `ORCHARD_REDIS_HOST`, `ORCHARD_REDIS_PORT`, `ORCHARD_REDIS_ENABLED`
+  - `ORCHARD_CACHE_TTL_INDEX`, `ORCHARD_CACHE_TTL_VERSIONS`, etc.
 - Added transparent PyPI proxy implementing PEP 503 Simple API (#108)
   - `GET /pypi/simple/` - package index (proxied from upstream)
   - `GET /pypi/simple/{package}/` - version list with rewritten download links
@@ -16,6 +33,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added `POST /api/v1/cache/resolve` endpoint to cache packages by coordinates instead of URL (#108)
 
 ### Changed
+- PyPI proxy now uses shared HTTP connection pool instead of per-request clients
+- PyPI proxy now caches upstream source configuration in Redis
+- Dependency storage now uses batch INSERT instead of individual queries
+- Increased default database pool size from 5 to 20 connections
+- Increased default database max overflow from 10 to 30 connections
+- Enabled Redis in Helm chart values for dev, stage, and prod environments
 - Upstream sources table text is now centered under column headers (#108)
 - ENV badge now appears inline with source name instead of separate column (#108)
 - Test and Edit buttons now have more prominent button styling (#108)