fix: code quality hardening — unwrap removal, unsafe forbid, Go/Raw tests (#72)

* fix: remove unwrap() from production code, improve error handling

- Replace unwrap() with proper error handling in npm, mirror, validation
- Add input validation to cargo registry (crate name + version)
- Improve expect() messages with descriptive context in metrics, rate_limit
- Remove unnecessary clone() in error.rs, docker.rs, npm.rs, dashboard_metrics
- Add #![deny(clippy::unwrap_used)] to prevent future unwrap in prod code
- Add let-else pattern for safer null checks in validation.rs

* docs: update SECURITY.md — add 0.3.x to supported versions

* security: forbid unsafe code at crate level

Add #![forbid(unsafe_code)] to both lib.rs and main.rs.
NORA has zero unsafe blocks — this prevents future additions
without removing the forbid attribute (stronger than deny).

* build: add rust-toolchain.toml, Dockerfile HEALTHCHECK

- Pin toolchain to stable with clippy + rustfmt components
- Add Docker HEALTHCHECK for standalone deployments (wget /health)

* test: add Go proxy and Raw registry integration tests

Go proxy tests: list, .info, .mod, @latest, path traversal, 404
Raw registry tests: upload/download, HEAD, 404, path traversal,
overwrite, delete, binary data (10KB)

nora-registry/src/metrics.rs

@@ -26,7 +26,7 @@ lazy_static! {
         "nora_http_requests_total",
         "Total number of HTTP requests",
         &["registry", "method", "status"]
-    ).expect("metric can be created");
+    ).expect("failed to create HTTP_REQUESTS_TOTAL metric at startup");
 
     /// HTTP request duration histogram
     pub static ref HTTP_REQUEST_DURATION: HistogramVec = register_histogram_vec!(
@@ -34,28 +34,28 @@ lazy_static! {
         "HTTP request latency in seconds",
         &["registry", "method"],
         vec![0.001, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, 10.0]
-    ).expect("metric can be created");
+    ).expect("failed to create HTTP_REQUEST_DURATION metric at startup");
 
     /// Cache requests counter (hit/miss)
     pub static ref CACHE_REQUESTS: IntCounterVec = register_int_counter_vec!(
         "nora_cache_requests_total",
         "Total cache requests",
         &["registry", "result"]
-    ).expect("metric can be created");
+    ).expect("failed to create CACHE_REQUESTS metric at startup");
 
     /// Storage operations counter
     pub static ref STORAGE_OPERATIONS: IntCounterVec = register_int_counter_vec!(
         "nora_storage_operations_total",
         "Total storage operations",
         &["operation", "status"]
-    ).expect("metric can be created");
+    ).expect("failed to create STORAGE_OPERATIONS metric at startup");
 
     /// Artifacts count by registry
     pub static ref ARTIFACTS_TOTAL: IntCounterVec = register_int_counter_vec!(
         "nora_artifacts_total",
         "Total artifacts stored",
         &["registry"]
-    ).expect("metric can be created");
+    ).expect("failed to create ARTIFACTS_TOTAL metric at startup");
 }
 
 /// Routes for metrics endpoint