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/modes/common.rs

@@ -21,7 +21,6 @@ use chrono::{DateTime, Utc};
 use clap::Command;
 use clap::error::ErrorKind;
 use comfy_table::{Attribute, Cell, ContentArrangement, Table};
-use lazy_static::lazy_static;
 use log::debug;
 use regex::Regex;
 use serde::{Deserialize, Serialize};
@@ -57,9 +56,8 @@ pub enum OutputFormat {
     Yaml,
 }
 
-lazy_static! {
-    static ref KEEP_META_RE: Regex = Regex::new(r"^KEEP_META_(.+)$").unwrap();
-}
+static KEEP_META_RE: std::sync::LazyLock<Regex> =
+    std::sync::LazyLock::new(|| Regex::new(r"^KEEP_META_(.+)$").unwrap());
 
 pub const IMPORT_FORMAT_ERROR: &str =
     "Unsupported import format: {} (expected .keep.tar or .meta.yml)";