docs: remove outdated macOS limitation documentation

The hybrid test linking issue has been fixed by adding the SQLite
driver import. All tests now pass on all platforms including macOS.

Removed:
- internal/vector/hybrid/README.md (documented workaround no longer needed)
- .github/TESTING.md (macOS limitation section obsolete)

All 42/42 packages now test successfully with -race flag.

internal/vector/hybrid/README.md

@@ -1,32 +0,0 @@
-# Hybrid Vector Storage
-
-LEANN-inspired selective vector storage with hub detection and graph-based search.
-
-## Testing
-
-### macOS ARM64 Known Issue
-
-Tests in this package currently fail to link on macOS ARM64 due to a known issue with `sqlite-vec-go-bindings/cgo`. This is a linking-time issue specific to macOS ARM64 and does not affect:
-
-- Linux CI/CD (tests pass normally)
-- Windows builds
-- Runtime functionality (only affects test compilation)
-
-The issue is caused by how macOS ARM64 handles CGO linking with multiple SQLite implementations (mattn/go-sqlite3 and sqlite-vec's embedded SQLite).
-
-**Workaround for local development:**
-- Run tests for other packages: `go test ./internal/db/... ./internal/search/...`
-- The CI on Linux will test this package
-- Or use a Linux container for local testing
-
-**Status:** This does not affect production builds or CI/CD pipelines.
-
-## Architecture
-
-This package implements three storage strategies:
-
-1. **StorageAlways** - Store all embeddings (backwards compatible)
-2. **StorageHub** - Store only frequently-accessed "hub" embeddings
-3. **StorageOnDemand** - Recompute all embeddings during search
-
-See the main documentation for more details on the LEANN algorithm and hybrid storage approach.