feat(schema): bump schemars to 1.x; round-trip + Draft-2020-12 tests (#5)

Chunk M1-W1-C of M1 plan — closes Plan §6.1.

Workspace dep:
- schemars 0.8 → 1 (latest 1.2.1; MSRV 1.74 stays well below our 1.85
  pin). 1.x emits Draft 2020-12 by default; the existing JsonSchema
  derives compile unchanged.

pearlite-schema dev-dep:
- serde_json (workspace dep, used only in tests).

Two acceptance tests in lib.rs::cross_cutting_tests:

- schemars_output_is_draft_2020_12 — generates the JSON Schema for
  DeclaredState and asserts the $schema field claims Draft 2020-12.
  This is the Plan §6.1 "schema: schemars_output_is_2020_12" gate.
- declared_state_round_trips_through_toml — parses host_full.toml,
  serializes it back, re-parses, and asserts equality. This is the
  "round-trip: declared_state_serde — every field round-trips through
  TOML" gate.

Plan §6.1 "Done when" status now:

- Public types derive Serialize, Deserialize, JsonSchema, Debug,
  Clone (+Eq/PartialEq/Hash/Default where applicable). ✓
- cargo doc --no-deps emits zero "missing docs" warnings. ✓
- A representative resolved.toml fixture round-trips without loss. ✓
- schemars output validates as Draft 2020-12. ✓
- Zero unwrap()/expect()/panic! in production code paths. ✓ (lints
  enforce workspace-wide).
- pearlite-audit reports no §13 violations. ✓

What's NOT in this chunk (deferred per Plan §6.1):
- Property tests with proptest — Plan §6.1 doesn't list any property
  test for pearlite-schema (proptest gates apply to pearlite-state §6.2
  and pearlite-diff §6.3).

Verification:
- cargo test -p pearlite-schema  (14 passed; 0 failed)
- cargo doc -p pearlite-schema --no-deps  (zero warnings)
- cargo clippy --workspace --all-targets -- -D warnings  (zero warnings)
- cargo fmt --all --check
- scripts/ci/check-spdx.sh
- pearlite-audit check .  (1 check, 0 violations)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: UnbreakableMJ

Cargo.lock

@@ -36,7 +36,7 @@ time = { version = "0.3", features = ["serde", "formatting", "parsing", "serde-w
 tracing = "0.1"
 tracing-subscriber = "0.3"
 clap = { version = "4", features = ["derive", "env", "wrap_help"] }
-schemars = "0.8"
+schemars = "1"
 sha2 = "0.10"
 tempfile = "3"
 rayon = "1"

Cargo.toml

@@ -17,3 +17,6 @@ toml = { workspace = true }
 time = { workspace = true }
 schemars = { workspace = true }
 thiserror = { workspace = true }
+
+[dev-dependencies]
+serde_json = { workspace = true }

crates/pearlite-schema/Cargo.toml

@@ -36,3 +36,41 @@ pub use services::ServicesDecl;
 pub use snapshots::SnapshotPolicy;
 pub use users::{HomeManagerDecl, HomeManagerMode, UserDecl};
 pub use validate::validate;
+
+#[cfg(test)]
+#[allow(
+    clippy::expect_used,
+    clippy::unwrap_used,
+    clippy::panic,
+    reason = "tests may use expect()/unwrap()/panic!() per Plan §4.2 + CLAUDE.md"
+)]
+mod cross_cutting_tests {
+    use super::*;
+
+    const FULL: &str = include_str!("../../../fixtures/schema/host_full.toml");
+
+    /// Plan §6.1 acceptance: emitted JSON Schema is Draft 2020-12.
+    #[test]
+    fn schemars_output_is_draft_2020_12() {
+        let schema = schemars::schema_for!(DeclaredState);
+        let json = serde_json::to_value(&schema).expect("serialize schema");
+        let dollar_schema = json
+            .get("$schema")
+            .and_then(|v| v.as_str())
+            .expect("$schema field present in emitted JSON Schema");
+        assert!(
+            dollar_schema.contains("2020-12"),
+            "expected Draft 2020-12, got: {dollar_schema}"
+        );
+    }
+
+    /// Plan §6.1 acceptance: a representative resolved.toml fixture
+    /// round-trips without loss.
+    #[test]
+    fn declared_state_round_trips_through_toml() {
+        let original = from_resolved_toml(FULL).expect("parse full fixture");
+        let serialized = toml::to_string(&original).expect("serialize");
+        let reparsed = from_resolved_toml(&serialized).expect("re-parse serialized");
+        assert_eq!(original, reparsed, "TOML round-trip must be lossless");
+    }
+}