Improve error message when removing a workshop twice

[jonathan-conder]

Description

This is a minor API break: v1PostProjectWorkshop returns 404 when a workshop isn't found. TBH not sure if this is a good idea.

Before:

$ workshop remove dev
error: cannot remove "dev": workshop not launched

After:

$ workshop remove dev
error: cannot remove "dev": workshop already removed

The intent of not launched is to hint that the user should launch the workshop; in this case that doesn't apply.

Self-review quick check

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// one way to handle errors
if err := f(); err != nil {
   ...
}

// one way to handle multiple returns
val, err := f()
if err != nil {
   ...
}
...

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Or:

• I confirm the PR has no implications for documentation.

[Copilot]

Pull request overview

Improves removal errors when the requested workshop is already absent.

Changes:

• Wraps ErrWorkshopNotLaunched with a clearer removal-specific message.
• Updates API test expectations for the new message.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
internal/overlord/workshopstate/manifest.go	Adds the removal-specific wrapped error.
internal/daemon/api_workshops_test.go	Updates expected API errors.

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[vikorama]

What would it say when the workshop has never been launched (hence never been removed)?

Cross-posting my MM proposal here:

I'd suggest to output a non-error message
"nimble" status is Off; nothing to remove.

When a user tries to remove several workshops, it'll be
"nimble" status is Off; nothing to remove
"jazzy" removed

The current error should stay as is when the status is pending.