chore(deps): update schemars to 0.9

[james-crabnebula]

Summary

• Updates schemars from 0.8 to 0.9 (identical to 1.0.0-alpha.18)
• Feature rename: url → url2 in workspace Cargo.toml
• Regenerated schema.json files: JSON Schema Draft 7 → 2020-12 (definitions → $defs, updated $schema URL)
• No Rust code changes — schema files regenerated automatically by existing build.rs

Test plan

• cargo fmt --check clean
• cargo clippy clean (all platforms)
• cargo test --workspace --all-targets — 5/5 on macOS, Linux, Windows
• cargo audit clean
• cargo deny check clean
• Lockfile diff reviewed — only schemars + schemars_derive swapped, serde_json gains indexmap (for preserve_order)

Supersedes #349 (Renovate PR only bumped version, missed the url → url2 feature rename).