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/args.rs

@@ -29,9 +29,7 @@ pub struct ModeArgs {
     pub save: bool,
 
     #[arg(group("mode"), help_heading("Mode Options"), short, long, conflicts_with_all(["save", "diff", "list", "delete", "info", "update", "status", "export", "import"]))]
-    #[arg(help(
-        "Get an item either by it's ID or by a combination of matching tags and metatdata"
-    ))]
+    #[arg(help("Get an item either by its ID or by a combination of matching tags and metadata"))]
     pub get: bool,
 
     #[arg(group("mode"), help_heading("Mode Options"), long, conflicts_with_all(["save", "get", "list", "delete", "info", "update", "status", "export", "import"]))]
@@ -48,9 +46,7 @@ pub struct ModeArgs {
     pub delete: bool,
 
     #[arg(group("mode"), help_heading("Mode Options"), short, long, conflicts_with_all(["save", "get", "diff", "list", "delete", "update", "status", "export", "import"]))]
-    #[arg(help(
-        "Get an item either by it's ID or by a combination of matching tags and metatdata"
-    ))]
+    #[arg(help("Get an item either by its ID or by a combination of matching tags and metadata"))]
     pub info: bool,
 
     #[arg(group("mode"), help_heading("Mode Options"), short('u'), long, conflicts_with_all(["save", "get", "diff", "list", "delete", "info", "status", "export", "import"]))]