chore: code review cleanup — fixes, deps, docs

Fixed:
- CLI help typo: "metatdata" -> "metadata"
- Filter buffer OOM: check size before loading into memory

Changed:
- #[inline] on HTML escape helpers for hot path performance
- Replaced once_cell and lazy_static with std::sync::LazyLock
- Removed unused once_cell and lazy_static crate dependencies

Refactored:
- Added module-level doc to services/ module

Documentation:
- README.md: zstd is native not external, "none" -> "raw"
- DESIGN.md: current schema and meta plugins section
- CHANGELOG.md: Unreleased section populated

src/meta_plugin/mod.rs

@@ -1,5 +1,4 @@
 use log::{debug, warn};
-use once_cell::sync::Lazy;
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 use std::sync::{Arc, Mutex};
@@ -444,9 +443,9 @@ where
     ///
     /// An empty `HashMap` (default implementation).
     fn outputs(&self) -> &std::collections::HashMap<String, serde_yaml::Value> {
-        use once_cell::sync::Lazy;
-        static EMPTY: Lazy<std::collections::HashMap<String, serde_yaml::Value>> =
-            Lazy::new(std::collections::HashMap::new);
+        use std::sync::LazyLock;
+        static EMPTY: LazyLock<std::collections::HashMap<String, serde_yaml::Value>> =
+            LazyLock::new(std::collections::HashMap::new);
         &EMPTY
     }
 
@@ -471,9 +470,9 @@ where
     ///
     /// An empty `HashMap` (default implementation).
     fn options(&self) -> &std::collections::HashMap<String, serde_yaml::Value> {
-        use once_cell::sync::Lazy;
-        static EMPTY: Lazy<std::collections::HashMap<String, serde_yaml::Value>> =
-            Lazy::new(std::collections::HashMap::new);
+        use std::sync::LazyLock;
+        static EMPTY: LazyLock<std::collections::HashMap<String, serde_yaml::Value>> =
+            LazyLock::new(std::collections::HashMap::new);
         &EMPTY
     }
 
@@ -602,8 +601,9 @@ where
 }
 
 /// Global registry for meta plugins.
-static META_PLUGIN_REGISTRY: Lazy<Mutex<HashMap<MetaPluginType, PluginConstructor>>> =
-    Lazy::new(|| Mutex::new(HashMap::new()));
+static META_PLUGIN_REGISTRY: std::sync::LazyLock<
+    Mutex<HashMap<MetaPluginType, PluginConstructor>>,
+> = std::sync::LazyLock::new(|| Mutex::new(HashMap::new()));
 
 /// Register a meta plugin with the global registry.
 ///