feat: npm full proxy — URL rewriting, scoped packages, publish, integrity cache (v0.2.31)

npm proxy:
- Rewrite tarball URLs in metadata to point to NORA (was broken — tarballs bypassed NORA)
- Scoped packages (@scope/package) full support in handler and repo index
- Metadata cache TTL (NORA_NPM_METADATA_TTL, default 300s) with stale-while-revalidate
- proxy_auth now wired into fetch_from_proxy (was configured but unused)

npm publish:
- PUT /npm/{package} — accepts standard npm publish payload
- Version immutability — 409 Conflict on duplicate version
- Tarball URL rewriting in published metadata

Security:
- SHA256 integrity verification on cached tarballs (immutable cache)
- Attachment filename validation (path traversal protection)
- Package name mismatch detection (URL vs payload)

Config:
- npm.metadata_ttl — configurable cache TTL (env: NORA_NPM_METADATA_TTL)

nora-registry/src/config.rs

@@ -112,6 +112,9 @@ pub struct NpmConfig {
     pub proxy_auth: Option<String>, // "user:pass" for basic auth
     #[serde(default = "default_timeout")]
     pub proxy_timeout: u64,
+    /// Metadata cache TTL in seconds (default: 300 = 5 min). Set to 0 to cache forever.
+    #[serde(default = "default_metadata_ttl")]
+    pub metadata_ttl: u64,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -215,6 +218,10 @@ fn default_timeout() -> u64 {
     30
 }
 
+fn default_metadata_ttl() -> u64 {
+    300 // 5 minutes
+}
+
 impl Default for MavenConfig {
     fn default() -> Self {
         Self {
@@ -232,6 +239,7 @@ impl Default for NpmConfig {
             proxy: Some("https://registry.npmjs.org".to_string()),
             proxy_auth: None,
             proxy_timeout: 30,
+            metadata_ttl: 300,
         }
     }
 }
@@ -486,6 +494,11 @@ impl Config {
                 self.npm.proxy_timeout = timeout;
             }
         }
+        if let Ok(val) = env::var("NORA_NPM_METADATA_TTL") {
+            if let Ok(ttl) = val.parse() {
+                self.npm.metadata_ttl = ttl;
+            }
+        }
 
         // npm proxy auth
         if let Ok(val) = env::var("NORA_NPM_PROXY_AUTH") {