[azure.ai.connection] leaks projectctx debug log to terminal on every command

[hund030]

Summary

Every azd ai connection <command> invocation prints an internal diagnostic line
to the terminal:

projectctx: resolved endpoint=https://<...>.services.ai.azure.com/api/projects/<proj> source=flag

This is developer-facing noise that users should never see. It appears
unconditionally — there is no --debug flag required to trigger it.

Repro

1. Install the azure.ai.connections extension.
2. Run any connection command against a Foundry project, e.g.:

   azd ai connection list -p https://<your-project-endpoint>
   

Expected

No projectctx: diagnostic line in normal output.

Actual

The projectctx: resolved endpoint=... source=... line is printed on every run.

Root cause

resolveConnectionContext in
cli/azd/extensions/azure.ai.connections/internal/cmd/connection_context.go
calls log.Printf("projectctx: resolved endpoint=%s source=%s", ...). The
extension never silences Go's default logger, so the line goes straight to the
terminal.

Beyond the noise, this is also a layering issue: endpoint resolution is owned by
projectctx.Resolve. Any such diagnostic belongs inside the projectctx
package (where the resolution decision is made), not in the consuming caller.

Fix

Remove the log.Printf line (and the now-unused log import) from
connection_context.go.