Derive CLI value lists from library enums with analyzer drift guard

[sdairs]

Closes #291.

Summary

Replace eight hand-maintained KNOWN_* constant lists in the CLI with pub const VALUES on the library enums they validate against. The analyzer now verifies that any enum declaring a VALUES const has it exactly equal (as a set) to its non-catch-all wire values, producing FindingKind::EnumValuesMismatch on mismatch.

This closes the drift chain: spec ↔ enum variants (guarded since #290) and enum variants ↔ VALUES (new check), so VALUES is transitively spec-accurate. A spec drift remediation that adds an enum value now flows automatically: spec → analyzer finding → models.rs variant + VALUES (analyzer fails CI if VALUES is not updated) → CLI validation, error messages, and --help update with zero CLI edits.

Changes

Library (models.rs)

• Add pub const VALUES: &'static [&'static str] to 9 enums: PgHaType, PgProvider, PgVersion, ServicePatchRequestReleasechannel, ServicePostRequestCompliancetype, ServicePostRequestProfile, ServicePostRequestProvider, ServicePostRequestRegion, ServicePostRequestReleasechannel.
• VALUES on ServicePostRequestRegion includes europe-west2 and ca-central-1, fixing existing drift where the CLI rejected valid regions.

Analyzer (clickhouse-openapi-analyzer)

• rust_inventory.rs: Parse Item::Impl blocks in models.rs to extract VALUES const string literals into EnumInfo.values_const. 4 new inventory tests.
• report.rs: Add FindingKind::EnumValuesMismatch, bump REPORT_SCHEMA_VERSION from 1 to 2.
• compare.rs: compare_enum_values_consts checks every enum with a VALUES const against its wire values (set equality); emits EnumValuesMismatch with details[missing] and details[extra]. 4 focused comparison tests.

Python issue rendering

• check-openapi-drift.py: Schema version check → 2, summary table row and simple_sections entry for enum_values_mismatch.
• test_check_openapi_drift.py: Synthetic finding, assertion, and schema version rejection test updated.

CLI (clickhousectl)

• commands.rs: Delete KNOWN_PROVIDERS, KNOWN_REGIONS, KNOWN_RELEASE_CHANNELS, KNOWN_COMPLIANCE_TYPES, KNOWN_PROFILES; use Enum::VALUES in parse_serde_enum calls.
• postgres.rs: Delete KNOWN_PG_PROVIDERS, KNOWN_PG_VERSIONS, KNOWN_PG_HA_TYPES; use Enum::VALUES in parse_serde_enum and PossibleValuesParser calls.

Documentation

• AGENTS.md: Added VALUES const checking section under enum value coverage.

Verification

cargo test --workspace                    # 720+ tests, 0 failures
cargo clippy --workspace --all-targets -- -D warnings   # clean
cargo check --workspace --all-features    # clean
python3 -m unittest discover -s scripts/tests -p 'test_*.py'  # 3 tests pass
python3 scripts/check-openapi-drift.py --dry-run          # 0 actionable drift

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