Parse positional server names on start

[sdairs]

Closes #357

Summary

• accept the ClickHouse server name positionally for local server start, matching stop and remove
• retain documented --name compatibility with a clear conflict when both forms are supplied
• require -- before clickhouse-server passthrough arguments so later clickhousectl flags remain parseable
• document the command contract and add clap plus subprocess regression coverage

Tests

• cargo fmt --all
• cargo test -p clickhousectl local::cli::tests
• cargo test -p clickhousectl --test local_server_start_args_test
• cargo test -p clickhousectl
• cargo clippy -p clickhousectl --all-targets -- -D warnings

[Copilot]

Pull request overview

This PR fixes clickhousectl local server start argument parsing to align with server stop/remove and prevent clickhousectl flags (e.g. --version) from being silently forwarded as ClickHouse server args. It introduces a positional server name for start, preserves --name for compatibility with an explicit conflict, and requires -- to begin clickhouse-server passthrough arguments.

Changes:

• Accept optional positional server name for local server start, while keeping --name as a compatible alternative (mutually exclusive).
• Change clickhouse-server passthrough parsing so arguments must be provided after -- (keeping clickhousectl flags parseable).
• Add clap parsing regression tests and a subprocess-level regression test covering the original issue scenario.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
README.md	Updates documentation/examples for positional server name and -- passthrough boundary.
crates/clickhousectl/src/local/cli.rs	Adjusts clap definitions for server start (positional name, --name compatibility, -- passthrough) and adds parsing tests.
crates/clickhousectl/src/local/mod.rs	Wires the two naming forms together (name.or(name_flag)) before calling start_server.
crates/clickhousectl/tests/local_server_start_args_test.rs	Adds subprocess regression coverage ensuring positional name doesn’t swallow --version and passthrough args remain isolated.

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