Validate cloud postgres list --filter keys and values

[sdairs]

Fixes #603.

Stacked PR: base is feat/615-postgres-delete-force, not main.

What was broken

cloud postgres list --filter matched keys with a catch-all _ => true, so any key outside {state, region, name, provider} — including isPrimary, which the listing shows as the Primary column — silently returned the whole unfiltered list with exit 0. A filter with an empty value (state=) or no = at all was ignored the same way. The state and provider predicates also compared format!("{:?}", ..) Debug forms against the wire value, so an Unknown(..) state could never match.

What changed

• --filter is parsed at clap time by a value_parser into a closed PostgresListFilter enum. An unknown key, a missing =, an empty/whitespace-only value, or a non-boolean isPrimary is now a usage error (exit 2) whose message lists the valid keys — and no API request is issued.
• isPrimary is a supported key (true/false, plus the yes/no the Primary column renders).
• state and provider are compared against the serde wire value via Display, case-insensitively, so multi-word states and Unknown(..) values match correctly. region/name match exactly; keys themselves are case-insensitive.
• Per CLAUDE.md, an absent (API-omitted) response field matches no filter value, and all filters must hold for an item to be kept.
• README documents the supported keys, the matching rules and the exit-2 behaviour.

cloud service list --filter is not affected: it forwards server-side resource-tag filters (tag:env=production) to the API as query parameters and shares none of this code, so client-side key validation there would wrongly reject valid server-side syntax.

Tests

• Clap parse tests next to the command definition: the accepted forms (including case-insensitive keys and yes/no), and one test per rejection asserting ErrorKind::ValueValidation and exit_code() == 2.
• Inline apply_filter tests: wire-value comparison for state/provider (including Restoring_backup and Unknown(..)), absent fields matching nothing, multi-filter conjunction, and the empty-filter passthrough.
• tests/cli_request_shape_test.rs: subprocess + wiremock tests pinning exit 2 with an expect(0) mock for invalid filters (no API call, no stdout), and the client-side filtering results for isPrimary, state=restoring_backup, region and a non-matching name.

Verified with cargo fmt --all, cargo clippy --workspace --all-targets -- -D warnings, and cargo test -p clickhousectl (all green). The clickhouse-cloud-api crate is untouched.

🤖 Generated with Claude Code

[iskakaushik]

LGTM