Make omitted local server selection deliberate

[sdairs]

Summary

• select default or a sole ClickHouse server deliberately for an omitted server stop name, with a typed zero-server no-op
• keep omitted server remove conservative and add path-safe human/JSON selection guidance
• preserve positional and --name dispatch while marking implicit and explicit outcomes
• document the selection policy and cover zero/one/many, running/stopped, default/custom, legacy, and persisted state

Tests

• cargo test -p clickhousectl --test local_server_selection_test
• cargo test -p clickhousectl --test local_server_name_compatibility_test
• cargo test -p clickhousectl --test local_server_stopped_test
• cargo test -p clickhousectl --test local_structured_errors_test
• cargo test -p clickhousectl -- --test-threads=1
• cargo fmt --all --check
• cargo clippy -p clickhousectl --all-targets -- -D warnings

Closes #473

[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

There are 3 total unresolved issues (including 2 from previous reviews).

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[sdairs]

Carry-over review from PR #514 (old PR for #473). This PR is preferred as the base: better dispatch modeling (ServerNameInput { Omitted, Positional, NameFlag } preserves how the name was supplied), better ordering (lock → recover → enumerate), implicit/explicit selection markers in both human and JSON output directly satisfy the acceptance criteria, and {available} counts in guidance. #514 should be closed in favor of it. But this PR regresses all five of sdairs' help-trim comments on #514 and has scope creep. Required:

1. Re-apply sdairs' five Make omitted local server selection deliberate #514 help trims verbatim (all regress here). On Make omitted local server selection deliberate #514, sdairs left five pending inline comments on crates/clickhousectl/src/local/cli.rs, all trimming help over-engineering; he then fixed them in commit 299d3b9 ("Trim local teardown help"): removed --name prose, hid the --name flag (hide = true), removed the "Idempotent…"/"typos" lines, and added a test asserting help never contains --name. In this PR:

   • cli.rs:~422-423 and cli.rs:~468-469 still carry "The compatibility form --name dev remains accepted, but cannot be combined with a positional name." → delete.
   • cli.rs:~427-428 still carry "Idempotent: a server that exists but is already stopped exits 0 (no error)." and "An unknown server name still errors so typos are caught." → delete (sdairs marked both "remove"/"uncessary - does not assist in operating the CLI").
   • The --name flags here are NOT hidden (cli.rs:~436, cli.rs:~479, no hide = true) → hide them.
   • Port the server_teardown_help_hides_compatibility_name_flags test asserting help never contains --name.

2. Revert omitted-name selection for stop --global. Make omitted local server selection deliberate #514 deliberately left --global stop unchanged (omitted name → literal default). This PR extends the selection policy to stop --global (mod.rs global arm), so an omitted global stop now stops a sole custom server in another project without a name — a real cross-project behavior change outside issue Make omitted local server name selection deliberate and actionable #473's scope (the issue is about project-scoped commands). Cursor Bugbot flagged "Global stop picks foreign sole server"; unanswered. Revert to fail-closed literal default, or explicitly justify the change in the PR description.

3. Fix Postgres-remnant selection pollution (regression of a Make omitted local server selection deliberate #514 fix). On Make omitted local server selection deliberate #514, sdairs fixed: an orphaned *-pg* data dir without metadata was miscounted as ClickHouse (commit a3e2b8e, with a regression test using a fake Docker socket proving a failed fresh Postgres start can't pollute ClickHouse selection). Here list_clickhouse_server_names_locked (server.rs:~414-434) counts such dirs again, and there is no equivalent test. Port the rollback fix (if not in this stack's base) and the fake-Docker regression test; add a Postgres-only project no-op exclusion case.

4. Document the new JSON error code. server_selection_required is emitted but the README structured-error table (head README.md:~978) still lists only the old codes; this PR's README diff doesn't touch the table. Add it (or remove the code if not kept).

5. Minor: selection is added to all stop/remove JSON output (including explicit calls, and Postgres outputs via selection: None) — a broader output-contract change than the issue requires; confirm intentional.

CI note: local postgres edge cases fails identically on both this and #514 — pre-existing stack-base breakage from #547, not this PR.