Add SSDP/UPnP scanner

Introduce a new SSDP/UPnP network scanner alongside the existing ARP and
mDNS scanners:

- New scanner module under scanners/ssdp (finder, scanner, status)
- Wire the scanner into the main scan loop
- Add Ssdp variant to DeviceEventScanner
- Add SsdpScanner settings with a configurable probe timeout
- Expose /api/ssdp_scanner/status and wire it into OpenAPI generation
- Add a lint.sh helper and point CLAUDE.md at it

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/settings.rs

@@ -41,6 +41,19 @@ impl Default for MdnsScanner {
     }
 }
 
+#[derive(Debug, Deserialize, Clone)]
+pub struct SsdpScanner {
+    pub probe_timeout: DurationString,
+}
+
+impl Default for SsdpScanner {
+    fn default() -> Self {
+        SsdpScanner {
+            probe_timeout: DurationString::try_from("2s".to_string()).unwrap(),
+        }
+    }
+}
+
 #[derive(Debug, Deserialize, Clone)]
 pub struct Pushover {
     pub token: String,
@@ -86,6 +99,8 @@ pub struct Settings {
     pub retention: Retention,
     #[serde(default)]
     pub mdns_scanner: MdnsScanner,
+    #[serde(default)]
+    pub ssdp_scanner: SsdpScanner,
 }
 // End configuration structure
 // -----------------------------------------------------------