feat(simulation): serve atlas layer requests over the bridge — completes #969 (D-225)

Closes the server-side layer-stream loop. serve_atlas_requests (PreInput) drains
the AtlasRequestBuffer and runs each through handle_atlas_request (cache hit ->
Ready; miss -> resolve via BodySourceResolver + enqueue an Immediate AnalyzeBody
-> Pending), buffering AtlasLayerResponses. send_atlas_responses (PostSnapshot)
flushes them to the client. main.rs wires BodySourceResolverResource (base root
= systems.db's 3rd ancestor; mod roots layer on later). Misses flow through the
#968 background tier and a re-request hits the now-warm cache.

Full path now live server-side: client request -> receive() demux -> serve ->
proxy -> (cache | queue+cascade) -> response -> client. The client half (send
request, decode response, render overlays) is #960.

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

server/src/main.rs

@@ -174,6 +174,30 @@ fn main() {
         }
     }
 
+    // Mod-first body source resolver for the atlas layer proxy (#969, D-225).
+    // terrain_reference is repo-root-relative; the repo root is systems.db's
+    // 3rd ancestor (<repo>/server/data/systems.db).
+    let world_root = systems_db_path
+        .canonicalize()
+        .ok()
+        .and_then(|p| p.ancestors().nth(3).map(std::path::Path::to_path_buf))
+        .unwrap_or_else(|| std::path::PathBuf::from(".."));
+    match settled_reach_server::atlas::source_resolver::BodySourceResolver::open(
+        &systems_db_path,
+        vec![world_root.clone()],
+    ) {
+        Ok(resolver) => {
+            tracing::info!("Body source resolver opened (root: {:?})", world_root);
+            app.insert_resource(
+                settled_reach_server::atlas::source_resolver::BodySourceResolverResource(resolver),
+            );
+        }
+        Err(e) => tracing::warn!(
+            "Body source resolver unavailable ({}). Atlas layer requests will error.",
+            e
+        ),
+    }
+
     // Initialize SQLite settings store (#627).
     // Path: alongside save files in the server's working directory.
     let settings_path = std::path::PathBuf::from("settings.db");