refactor: decouple meta plugins from DB via SaveMetaFn callback, extract shared utilities

- Add SaveMetaFn callback pattern: meta plugins receive a closure instead of
  &Connection, enabling the same plugin code to work in local, client, and
  server contexts (collect-to-Vec, collect-to-HashMap, or direct DB write)
- Client save now runs meta plugins locally during streaming (smart client
  sets meta=false, server skips its own plugins)
- Add POST /api/item/{id}/update endpoint for re-running plugins on stored
  content without downloading compressed data
- Add client update mode (--update with --meta-plugin flags)
- Extract shared utilities: stream_copy, print_serialized, build_path_table,
  ensure_default_tag to reduce duplication across modes
- Add upsert_tag for idempotent tag addition (INSERT OR IGNORE)
- Add warn logging on save_meta lock failure in BaseMetaPlugin and MetaService

src/modes/client/info.rs

@@ -31,11 +31,8 @@ pub fn mode(
         let item = client.get_item_info(id)?;
 
         match output_format {
-            OutputFormat::Json => {
-                println!("{}", serde_json::to_string_pretty(&item)?);
-            }
-            OutputFormat::Yaml => {
-                println!("{}", serde_yaml::to_string(&item)?);
+            OutputFormat::Json | OutputFormat::Yaml => {
+                crate::modes::common::print_serialized(&item, &output_format)?;
             }
             OutputFormat::Table => {
                 let display = DisplayItemInfo {