Context agent: expand module library

[bokelley]

Summary

• Add 6 new evaluation modules: EmbeddingMatch (cosine similarity), KeywordMatch (set intersection), BrandSafety (category blocklist), GeoFilter (allow/block lists), DaypartFilter (day-of-week + hour ranges), CatalogMatch (product catalog to content topics)
• Each module implements the Module interface, is independently configurable, and has thorough tests
• Add SMembers to ValkeyClient interface and MockValkeyClient
• Fix pre-existing lint issues in agent_test.go, main.go, and sync.go

Closes #4

Test plan

• 24 new tests across 6 test files, all passing with -race
• golangci-lint clean
• Existing tests still pass

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