Add global ~/.local/bin/clickhouse symlink on local use (#202)

[sdairs]

Summary

• clickhousectl local use <version> now creates/updates ~/.local/bin/clickhouse as a symlink to the active binary, so clickhouse local, clickhouse client, etc. work without going via clickhousectl. Opt-out with --no-global.
• local remove of the currently-default version also clears the symlink — but only if it still points into that version's directory, so a manually repointed link is preserved.
• If a regular file (not a symlink) already exists at the path, it's left alone with a stderr warning — no silent clobbering of a user-managed install.
• Unix-only via #[cfg(unix)]; non-unix builds get a no-op stub. Symlink failures are best-effort: they emit a stderr warning but never affect the command's exit status, so the default file always gets written.
• After a successful symlink, the helper warns once if ~/.local/bin is not on $PATH.

Closes #202.

Test plan

• cargo build -p clickhousectl — clean
• cargo test -p clickhousectl — 9 new unit tests + existing suite green
• cargo clippy -p clickhousectl --all-targets — no new warnings
• local use stable → symlink created at ~/.local/bin/clickhouse pointing at the binary
• local use lts --no-global → default updated, symlink unchanged
• local use lts → symlink retargeted to LTS
• Regular file at ~/.local/bin/clickhouse → warning printed, file untouched, default still set

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds a “global” clickhouse entrypoint when selecting a local default ClickHouse version, by managing a ~/.local/bin/clickhouse symlink during clickhousectl local use (opt-out via --no-global) and cleaning it up on local remove when appropriate. This fits the local version-management workflow by enabling direct clickhouse ... invocation without going through clickhousectl.

Changes:

• Add --no-global to clickhousectl local use and best-effort creation/update of ~/.local/bin/clickhouse symlink.
• Clear the global symlink on local remove of the active default version (only when it still points into that version’s directory).
• Document the behavior in the README and CLI help, and add a Unix-only symlink helper + unit tests.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
README.md	Documents the new global clickhouse symlink behavior and --no-global.
crates/clickhousectl/src/paths.rs	Adds helpers for ~/.local/bin and the clickhouse symlink path.
crates/clickhousectl/src/local/symlink.rs	Implements Unix-only symlink create/update/remove logic and unit tests.
crates/clickhousectl/src/local/mod.rs	Wires symlink management into local use and local remove.
crates/clickhousectl/src/local/cli.rs	Adds the --no-global flag and updates local use help text.

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