remove migrated .NET MEVD providers, add redirect READMEs

[Copilot]

Motivation and Context

All .NET MEVD vector store providers have been migrated to the CommunityToolkit/AI repository. This removes the now-redundant source code and tests from this repo and leaves discoverable redirects in their place.

Description

Removed source + tests for 12 providers (Chroma and Milvus kept unchanged):

• AzureAISearch, CosmosMongoDB, CosmosNoSql, InMemory, PgVector, Qdrant, Redis, SqlServer, SqliteVec, Weaviate → moved to CommunityToolkit/AI/MEVD/src/
• MongoDB → moved to mongodb/mongo-mevd-provider
• Pinecone → removed; Pinecone archived their .NET SDK, no longer supported
• Common → removed (was only shared by SqlServer/SqliteVec/PgVector, all gone)

Added README.md in each removed provider directory pointing to the new upstream location (or explaining Pinecone deprecation).

Removed all associated test projects including the shared VectorData.ConformanceTests infrastructure (no remaining consumers after provider removal).

Updated dotnet/MEVD.slnx — now contains only Chroma and Milvus.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[Adam Sitnik (adamsitnik)]

Copilot go over dotnet/Directory.Packages.props and remove the packages that we no longer need

[Copilot]

Copilot go over dotnet/Directory.Packages.props and remove the packages that we no longer need

Done. Removed the following packages that are no longer referenced anywhere in the codebase:

• Pinecone.Client
• SQLitePCLRaw.lib.e_sqlite3
• Azure.Search.Documents
• MongoDB.Driver
• Microsoft.Azure.Cosmos
• Pgvector
• sqlite-vec
• NRedisStack
• Microsoft.Data.Sqlite
• Microsoft.Data.SqlClient
• Qdrant.Client
• Testcontainers (base)
• Testcontainers.MsSql
• Testcontainers.PostgreSql
• Testcontainers.Qdrant
• Testcontainers.Redis

Kept: Npgsql (used in IntegrationTests + Concepts), Testcontainers.MongoDB (IntegrationTests), Testcontainers.Milvus (IntegrationTests + Process tests), CommunityToolkit.VectorData.* (samples + tests), Microsoft.Data.Sqlite was also verified gone — only SqliteVec used it.

Committed in 840c696's follow-up.

[Adam Sitnik (adamsitnik)]

The Community Toolkit AI repo is now public, so the code can be removed.

The CI is green, the PR is ready for review:

[Copilot]

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[Shay Rojansky (roji)]

Updated dotnet/MEVD.slnx — now contains only Chroma and Milvus.

Honestly, I'd remove these. IIRC they're pre-MEVD providers (so the old v1 vector store API), not maintained and unsupported. If we ever do want to redo a Chroma/Milvus provider we'd probably start from scratch anyway.