feat(dashboard): show version in header, restructure footer

Closes #108.

- Add `version` field to /stats (from CARGO_PKG_VERSION).
- Show `v0.13.1` next to the Numa wordmark in the dashboard header.
- Restructure the footer into two semantic rows:
  Row 1 (paths): Config · Data · Logs (platform-detected)
  Row 2 (runtime): Upstream · DNSSEC · SRTT · GitHub
- Drop Mode from the footer (redundant with Upstream label).
- Show only the matching-platform log path instead of both
  macOS and Linux unconditionally.

src/api.rs

@@ -160,6 +160,7 @@ struct QueryLogResponse {
 
 #[derive(Serialize)]
 struct StatsResponse {
+    version: &'static str,
     uptime_secs: u64,
     upstream: String,
     mode: &'static str, // "recursive" or "forward" — never "auto" at runtime
@@ -539,6 +540,7 @@ async fn stats(State(ctx): State<Arc<ServerCtx>>) -> Json<StatsResponse> {
     };
 
     Json(StatsResponse {
+        version: env!("CARGO_PKG_VERSION"),
         uptime_secs: snap.uptime_secs,
         upstream,
         mode: ctx.upstream_mode.as_str(),