fix(stop): add --name flag to stop named contexts and instances - #461

Problem

The microcks stop command only supports stopping the instance associated with the current context. There is no way to target a specific instance by name — even though microcks start --name <name> and microcks login --name <name> already allow users to create named contexts and instances.

This asymmetry means that after starting multiple instances or logging into multiple servers, users have no direct way to stop a specific one without first switching context.

Root Cause

When a user runs microcks start --name myinstance, the CLI stores the context with:

• Context name = http://localhost:8585 (the server URL)
• Instance field = myinstance (the user-given name)

So a naive lookup by context name alone (ResolveContext(myinstance)) fails — there is no context literally named myinstance. The existing ResolveContext expects the context's name field, not the Instance field.

Solution

This PR adds a --name flag to microcks stop with a two-tier fallback resolution:

1. Try as a context name — works for contexts created via microcks login --name dev (stored as Context{Name: "dev"})
2. Scan contexts by Instance field — works for contexts created via microcks start --name myinstance (stored as ContextRef{Name: "http://...", Instance: "myinstance"})

If neither lookup succeeds, the user receives a clear error message.

When --name is omitted, behavior is 100% identical to the current code (uses the current context).

Changes

cmd/stop.go — 29 insertions, 2 deletions:

• Added var name string for the flag variable
• Added Example help text with usage patterns
• Added two-tier context resolution logic
• Registered the --name flag on stopCmd

Verification

Example Usage

# Stop the instance from the current context (existing behavior)
microcks stop

# Stop by context name (useful after login --name)
microcks stop --name dev-context

# Stop by instance name (useful after start --name)
microcks stop --name myinstance

Fixes #438