feat(chroma): upgrade to chroma-go v0.3.x with Chroma Cloud support

[tazarov]

Summary of Changes

• Upgrade from legacy chroma-go API to v0.3.2 (pkg/api/v2)
• Add WithClient option for pre-configured client injection
• Add WithCloudAPIKey, WithTenant, WithDatabase options for Chroma Cloud - https://docs.trychroma.com/cloud/schema/overview
• Add Search() method using Chroma's Search API (relevance scores, pagination, read levels) - https://docs.trychroma.com/cloud/search-api/overview
• Add Collection() getter as escape hatch for advanced search patterns (RRF, grouping)
• Refactor New() to support three client modes: pre-configured, cloud, and HTTP
• Add rawWhereClause adapter for Search API filtering

PR Checklist

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