fix: add --meta filtering support to client/server list mode

Plumb metadata filter from client CLI through the HTTP API to the
server's data_service.list_items(). The server accepts a JSON-encoded
meta query parameter where null values mean 'key exists' and string
values mean 'exact match'.

Also fix LZ4 compression round-trip for client mode:
- Explicit flush FrameEncoder before drop to avoid sending only the
  frame header when compress=false
- Send _client_compression metadata so client knows actual compression
  on retrieval (server records compression=None when compress=false)
- Use FrameDecoder (frame format) instead of decompress_size_prepended
  (size-prepended format) to match server storage format

src/modes/client/info.rs

@@ -16,7 +16,7 @@ pub fn mode(
 
     // If tags provided, find matching item first
     let item_ids: Vec<i64> = if !tags.is_empty() {
-        let items = client.list_items(tags, "newest", 0, 1)?;
+        let items = client.list_items(tags, "newest", 0, 1, &std::collections::HashMap::new())?;
         if items.is_empty() {
             return Err(anyhow::anyhow!("No items found matching tags: {:?}", tags));
         }