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/filter_plugin/grep.rs

@@ -73,7 +73,7 @@ impl FilterPlugin for GrepFilter {
         for line in buf_reader.by_ref().lines() {
             let line = line?;
             if self.regex.is_match(&line) {
-                writeln!(writer, "{}", line)?;
+                writeln!(writer, "{line}")?;
             }
         }
         Ok(())

src/filter_plugin/head.rs

@@ -184,7 +184,7 @@ impl FilterPlugin for HeadLinesFilter {
         let mut buf_reader = std::io::BufReader::new(reader);
         for line in buf_reader.by_ref().lines() {
             let line = line?;
-            writeln!(writer, "{}", line)?;
+            writeln!(writer, "{line}")?;
             self.remaining -= 1;
             if self.remaining == 0 {
                 break;

src/filter_plugin/mod.rs

@@ -381,7 +381,7 @@ pub fn parse_filter_string(filter_str: &str) -> Result<FilterChain> {
                     _ => {
                         return Err(std::io::Error::new(
                             std::io::ErrorKind::InvalidInput,
-                            format!("Filter '{}' requires parameters", part),
+                            format!("Filter '{part}' requires parameters"),
                         ));
                     }
                 }
@@ -391,7 +391,7 @@ pub fn parse_filter_string(filter_str: &str) -> Result<FilterChain> {
         // If we get here, the filter wasn't recognized
         return Err(std::io::Error::new(
             std::io::ErrorKind::InvalidInput,
-            format!("Unknown filter: {}", part),
+            format!("Unknown filter: {part}"),
         ));
     }
 
@@ -454,7 +454,7 @@ fn create_filter_with_options(
         if !option_defs.iter().any(|opt| &opt.name == key) {
             return Err(std::io::Error::new(
                 std::io::ErrorKind::InvalidInput,
-                format!("Unknown option '{}'", key),
+                format!("Unknown option '{key}'"),
             ));
         }
         options.insert(key.clone(), value.clone());

src/filter_plugin/skip.rs

@@ -108,7 +108,7 @@ impl FilterPlugin for SkipLinesFilter {
             if self.remaining > 0 {
                 self.remaining -= 1;
             } else {
-                writeln!(writer, "{}", line)?;
+                writeln!(writer, "{line}")?;
             }
         }
         Ok(())

src/filter_plugin/tail.rs

@@ -127,7 +127,7 @@ impl FilterPlugin for TailLinesFilter {
 
         // Write the buffered lines
         for line in &self.lines {
-            writeln!(writer, "{}", line)?;
+            writeln!(writer, "{line}")?;
         }
         Ok(())
     }