Fix running server remove error message

[sdairs]

Closes #325

Summary

• report an actionable stop-first command when removing a running local server
• preserve the existing start collision wording

Tests

• cargo test -p clickhousectl --test local_server_stopped_test running_server_remove_has_stop_first_error_and_start_keeps_collision_error -- --exact
• cargo test -p clickhousectl
• cargo clippy -p clickhousectl --all-targets -- -D warnings

[Copilot]

Pull request overview

This PR fixes the error message shown when attempting to remove a running local ClickHouse server, making it actionable (“stop it first …”) while preserving the existing “already running” wording for server start name collisions. This aligns CLI behavior with issue #325’s expected UX without changing the underlying refusal-to-remove logic.

Changes:

• Introduce a dedicated error variant (ServerRunningCannotRemove) with a stop-first instruction.
• Update the local server remove handler to return the new error when the target server is running.
• Add an integration-style regression test covering both remove (new message) and start (existing collision message).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
crates/clickhousectl/tests/local_server_stopped_test.rs	Adds a regression test asserting the new stop-first remove error and unchanged start collision error.
crates/clickhousectl/src/local/mod.rs	Switches server remove to return the new “running; stop first” error variant when applicable.
crates/clickhousectl/src/error.rs	Adds ServerRunningCannotRemove with the expected actionable error message.

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