feat: health API — add build_timestamp + detailed resource status list

- build.rs: BUILD_TIMESTAMP from build time via `date -u`
- GET /health: now returns build_timestamp
- GET /health/detailed: returns build_timestamp + resources block
  (cpu_used/cpu_idle/memory/gpu usage)

build.rs

@@ -9,6 +9,15 @@ fn main() {
         .map(|s| s.trim().to_string())
         .unwrap_or_else(|| "unknown".to_string());
 
+    let timestamp = std::process::Command::new("date")
+        .args(["-u", "+%Y-%m-%dT%H:%M:%SZ"])
+        .output()
+        .ok()
+        .and_then(|o| String::from_utf8(o.stdout).ok())
+        .map(|s| s.trim().to_string())
+        .unwrap_or_else(|| "unknown".to_string());
+
     println!("cargo:rustc-env=BUILD_VERSION={}", version);
     println!("cargo:rustc-env=BUILD_GIT_HASH={}", git_hash);
+    println!("cargo:rustc-env=BUILD_TIMESTAMP={}", timestamp);
 }

src/api/server.rs

@@ -16,6 +16,7 @@ use crate::core::cache::{keys, MongoCache, RedisCache};
 use crate::core::config::REDIS_KEY_PREFIX;
 use crate::core::db::schema;
 use crate::core::db::{Database, PostgresDb, QdrantDb, RedisClient, VideoRecord, VideoStatus};
+use crate::worker::resources::SystemResources;
 use crate::core::text::tokenizer::tokenize_chinese_text;
 use crate::{Embedder, FileManager};
 
@@ -73,6 +74,7 @@ struct HealthResponse {
     status: String,
     version: String,
     build_git_hash: String,
+    build_timestamp: String,
     uptime_ms: u64,
 }
 
@@ -371,8 +373,22 @@ struct DetailedHealthResponse {
     status: String,
     version: String,
     build_git_hash: String,
+    build_timestamp: String,
     uptime_ms: u64,
     services: ServiceHealth,
+    resources: ResourceStatus,
+}
+
+#[derive(Debug, Serialize)]
+struct ResourceStatus {
+    cpu_used_percent: f64,
+    cpu_idle_percent: f64,
+    memory_available_mb: u64,
+    memory_total_mb: u64,
+    memory_used_percent: f64,
+    gpu_available: bool,
+    gpu_utilization: Option<f64>,
+    gpu_memory_used_pct: Option<f64>,
 }
 
 #[derive(Debug, Serialize)]
@@ -411,6 +427,7 @@ async fn health(State(state): State<AppState>) -> Json<HealthResponse> {
         status: status.to_string(),
         version: env!("BUILD_VERSION").to_string(),
         build_git_hash: env!("BUILD_GIT_HASH").to_string(),
+        build_timestamp: env!("BUILD_TIMESTAMP").to_string(),
         uptime_ms: get_uptime_ms(),
     })
 }
@@ -431,10 +448,13 @@ async fn health_detailed(State(state): State<AppState>) -> Json<DetailedHealthRe
         "degraded"
     };
 
+    let sys = SystemResources::check();
+
     Json(DetailedHealthResponse {
         status: overall_status.to_string(),
         version: env!("BUILD_VERSION").to_string(),
         build_git_hash: env!("BUILD_GIT_HASH").to_string(),
+        build_timestamp: env!("BUILD_TIMESTAMP").to_string(),
         uptime_ms: get_uptime_ms(),
         services: ServiceHealth {
             postgres,
@@ -442,6 +462,16 @@ async fn health_detailed(State(state): State<AppState>) -> Json<DetailedHealthRe
             qdrant,
             mongodb,
         },
+        resources: ResourceStatus {
+            cpu_used_percent: sys.cpu_used_percent,
+            cpu_idle_percent: sys.cpu_idle_percent,
+            memory_available_mb: sys.memory_available_mb,
+            memory_total_mb: sys.memory_total_mb,
+            memory_used_percent: sys.memory_used_percent,
+            gpu_available: sys.gpu_available,
+            gpu_utilization: sys.gpu_utilization,
+            gpu_memory_used_pct: sys.gpu_memory_used_pct,
+        },
     })
 }