feat: add config show command for active microcks context

the cli stores microcks connection details in the local config, but there is no simple command that shows what the active context currently points to. when debugging microcks import, microcks test, or local tooling that connects to microcks, users currently have to inspect the raw config file manually to confirm the current context, server url, tls setting, and whether auth credentials are present.

a microcks config show command would make that state visible from the cli without exposing secrets. the default output could print a small table with the current context name, server url, insecure tls setting, whether an auth token is present, whether a refresh token is present, and linked local instance information if the context has one.

example:

microcks config show

current context   server                  insecure tls   auth token   instance
local             http://localhost:8585   false          present      microcks

the first version can stay focused: add a config show command under cmd/, reuse the existing local config loading and context resolution code, mask token values instead of printing them, add tests with temporary config fixtures, and update command documentation.

this also supports the vs code integration work in #255 because editor tooling needs an easy way for users to confirm which microcks instance their local environment is configured to use.

Beginne unter cmd/ und verfolge das bestehende Laden der lokalen Konfiguration und die Kontextauflösung, die von der CLI verwendet werden. Füge den Einstiegspunkt für config show hinzu und untersuche die Tests der temporären Konfigurations-Fixtures, um Kontext, Server-URL, TLS, das Vorhandensein des Tokens, das Vorhandensein des Refresh-Tokens und Details zur verknüpften Instanz abzudecken, ohne Geheimnisse auszugeben. Aktualisiere die Befehlsdokumentation, sobald Ausgabe und Tests abgeschlossen sind.