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/compression_engine/program.rs

@@ -1,4 +1,4 @@
-use anyhow::{Context, Result, anyhow};
+use anyhow::{anyhow, Context, Result};
 use log::*;
 use std::fs::File;
 use std::io::{Read, Write};
@@ -94,16 +94,13 @@ impl CompressionEngine for CompressionEngineProgram {
         )
     }
 
-    fn open(&self, file_path: PathBuf) -> Result<Box<dyn Read>> {
-        debug!("COMPRESSION: Opening {:?} using {:?}", file_path, *self);
+    fn open(&self, file_path: PathBuf) -> Result<Box<dyn Read + Send>> {
+        debug!("COMPRESSION: Opening {file_path:?} using {self:?}");
 
         let program = self.program.clone();
         let args = self.decompress.clone();
 
-        debug!(
-            "COMPRESSION: Executing command: {:?} {:?} reading from {:?}",
-            program, args, file_path
-        );
+        debug!("COMPRESSION: Executing command: {program:?} {args:?} reading from {file_path:?}");
 
         let file = File::open(file_path).context("Unable to open file for reading")?;
 
@@ -130,15 +127,12 @@ impl CompressionEngine for CompressionEngineProgram {
     }
 
     fn create(&self, file_path: PathBuf) -> Result<Box<dyn Write>> {
-        debug!("COMPRESSION: Writing to {:?} using {:?}", file_path, *self);
+        debug!("COMPRESSION: Writing to {file_path:?} using {self:?}");
 
         let program = self.program.clone();
         let args = self.compress.clone();
 
-        debug!(
-            "COMPRESSION: Executing command: {:?} {:?} writing to {:?}",
-            program, args, file_path
-        );
+        debug!("COMPRESSION: Executing command: {program:?} {args:?} writing to {file_path:?}");
 
         let file = File::create(file_path).context("Unable to open file for writing")?;