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/services/types.rs

@@ -40,6 +40,15 @@ impl ItemWithMeta {
             .map(|m| (m.name, m.value))
             .collect()
     }
+
+    /// Returns a list of tag names for this item.
+    ///
+    /// # Returns
+    ///
+    /// `Vec<String>` - Tag names extracted from the tags list.
+    pub fn tag_names(&self) -> Vec<String> {
+        self.tags.iter().map(|t| t.name.clone()).collect()
+    }
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]