refactor: simplify cmd/metis imports and remove unused code

[meaningforger]

Summary

• Use package names directly where imports do not collide; keep only the MCP SDK and DuckDB fixture aliases needed for disambiguation.
• Remove unused request logging and a metrics route helper that production no longer calls.
• Delete the obsolete cmd/metis metrics test file and test the actual metrics route in app/hosting.

Validation

• go test ./cmd/metis ./app/hosting
• CGO_ENABLED=1 go test -tags duckdb ./cmd/metis ./app/hosting
• go run golang.org/x/tools/cmd/deadcode -test ./cmd/metis (no cmd/metis findings)
• CGO_ENABLED=1 go run golang.org/x/tools/cmd/deadcode -tags duckdb -test ./cmd/metis (no cmd/metis findings)
• git diff --check