[bugwz]

Summary

• Store ID-based Go SDK databases at .agentfs/{id}.db relative to the current working directory instead of ~/.agentfs/{id}.db.
• Update Go SDK comments and documentation to reflect the corrected path.
• Add regression coverage verifying that the database is created under the current working directory.

Motivation

The Rust, Python, and TypeScript SDKs, as well as the CLI and root documentation, consistently use .agentfs/{id}.db.

The Go SDK was the only implementation resolving ID-based databases under the user's home directory. As a result, the same agent ID could refer to different databases depending on which SDK was used.

Explicit paths supplied through AgentFSOptions.Path remain unchanged.

Testing

• go test ./...
• go vet ./...

[bugwz]

@penberg please CR~