fix: correct critical bugs and improve pipe streaming performance

Critical bug fixes:
- save_item now returns real Item from database, not a hardcoded fake
- AsyncDataService::save() reuses self.sync_service instead of creating redundant instance
- GenerateStatus trait signature mismatch fixed (CLI/API decoupling)

Performance improvements (pipe path untouched):
- CompressionEngine::open() returns Box<dyn Read + Send> enabling true streaming
- mode_get eliminates triple full-file read (was sampling then re-reading entire file)
- FilteringReader adds fast-path bypass when no filters, pre-allocates temp buffer
- text.rs meta plugin processes &[u8] slice directly, eliminates data.to_vec() clone

API correctness:
- Tag parse errors now return 400 instead of being silently discarded
- compute_diff uses similar crate (LCS-based) instead of naive positional comparison

Cleanup:
- Modernize string formatting (format!({x})) across codebase
- Remove redundant DB query in get mode
- Derive Debug/ToSchema on public types
- Delete placeholder test files with no real assertions
- Extract parse_comma_tags utility function

src/services/meta_service.rs

@@ -16,16 +16,13 @@ impl MetaService {
     pub fn get_plugins(&self, cmd: &mut Command, settings: &Settings) -> Vec<Box<dyn MetaPlugin>> {
         debug!("META_SERVICE: get_plugins called");
         let meta_plugin_types: Vec<MetaPluginType> = settings_meta_plugin_types(cmd, settings);
-        debug!(
-            "META_SERVICE: Meta plugin types from settings: {:?}",
-            meta_plugin_types
-        );
+        debug!("META_SERVICE: Meta plugin types from settings: {meta_plugin_types:?}");
 
         // Create plugins with their configuration
         let meta_plugins: Vec<Box<dyn MetaPlugin>> = meta_plugin_types
             .iter()
             .map(|meta_plugin_type| {
-                debug!("META_SERVICE: Creating plugin: {:?}", meta_plugin_type);
+                debug!("META_SERVICE: Creating plugin: {meta_plugin_type:?}");
 
                 // Get the plugin name using strum's Display implementation
                 let plugin_name = meta_plugin_type.to_string();
@@ -186,7 +183,7 @@ impl MetaService {
                 value: meta_data.value,
             };
             if let Err(e) = crate::db::store_meta(conn, db_meta) {
-                log::warn!("META_SERVICE: Failed to store metadata: {}", e);
+                log::warn!("META_SERVICE: Failed to store metadata: {e}");
             }
         }
     }