refactor: rename size to uncompressed_size, add compressed_size and closed columns

Schema changes:
- Rename items.size to items.uncompressed_size for clarity
- Add compressed_size (INTEGER NULL) - tracks compressed file size on disk
- Add closed (BOOLEAN NOT NULL DEFAULT 1) - tracks whether item is fully written
- Existing items default to closed=true via migration

Lifecycle:
- Items created with closed=false, set to true on successful save/import
- Compressed size captured via fs::metadata() after compression writer closes
- Truncated uploads (413) get compressed_size set, closed=true, uncompressed_size=None
- Update command now backfills both uncompressed_size and compressed_size

Also includes bug fixes and dedup from prior review:
- Fix stream_raw_content_response using uncompressed_size for raw byte Content-Length
- ApiResponse::ok()/empty() constructors, TryFrom<ItemWithMeta> for ItemInfo
- tag_names() method on ItemWithMeta, meta_filter() on Settings
- Fix .unwrap() panics in compression engine Read/Write impls
- Fix TOCTOU race in stream_raw_content_response (now uses compressed_size)
- Fix swallowed write errors in meta plugins (digest, magic_file, exec)
- Fix term::stderr().unwrap() panic in item_service
- Deduplicate ItemService::new() calls across 20 API handlers
- ImportMeta supports #[serde(alias = "size")] for backward compat

All 75 tests, 67 doc tests pass. Clippy clean.

src/modes/list.rs

@@ -152,7 +152,7 @@ pub fn mode_list(
                     .with_timezone(&chrono::Local)
                     .format("%F %T")
                     .to_string(),
-                ColumnType::Size => match item.size {
+                ColumnType::Size => match item.uncompressed_size {
                     Some(size) => format_size(size as u64, settings.human_readable),
                     None => match item_path.metadata() {
                         Ok(_) => "Unknown".to_string(),
@@ -218,7 +218,7 @@ pub fn mode_list(
             // Apply styling for specific cases
             match column_type {
                 ColumnType::Size => {
-                    if item.size.is_none() {
+                    if item.uncompressed_size.is_none() {
                         if item_path.metadata().is_ok() {
                             cell = cell
                                 .fg(comfy_table::Color::Yellow)
@@ -282,7 +282,7 @@ fn show_list_structured(
             None => "Missing".to_string(),
         };
 
-        let size_formatted = match item.size {
+        let size_formatted = match item.uncompressed_size {
             Some(size) => crate::modes::common::format_size(size as u64, settings.human_readable),
             None => "Unknown".to_string(),
         };
@@ -294,7 +294,7 @@ fn show_list_structured(
                 .with_timezone(&chrono::Local)
                 .format("%F %T")
                 .to_string(),
-            size: item.size.map(|s| s as u64),
+            size: item.uncompressed_size.map(|s| s as u64),
             size_formatted,
             compression: item.compression,
             file_size,