fix(komga): fix EPUB manifest metadata serialization breaking Komic TOC display

Rust's Decimal type serializes as a JSON string ("1") rather than a number (1),
which caused Readium's strict metadata parser to silently reject the entire
manifest in Komic, preventing the table of contents from displaying.

Key changes:
- Convert Decimal position to f64/i64 before JSON serialization to emit numbers
- Build absolute URLs using X-Forwarded-Proto/Host headers for reverse proxy support
- Add belongsTo (series info), language, modified, ISBN identifier to metadata
- Add /manifest route alias alongside /manifest/epub (Komga serves both)
- Add thumbnail entry to resources list
- Rewrite NCX parser with proper navPoint depth tracking via find_closing_nav_point
- Add NCX fallback discovery by well-known item IDs (toc, ncx, ncxtoc)
- Add EPUB 3 nav document parser for modern EPUBs
- Add tests for NCX parsing (flat, nested, real EPUB)

Author: AshDevFr

src/api/routes/komga/dto/manifest.rs

@@ -10,6 +10,7 @@ use utoipa::ToSchema;
 ///
 /// Root structure for the manifest returned by the EPUB manifest endpoint.
 /// Matches Komga's WebPub Manifest output for maximum compatibility.
+#[allow(dead_code)]
 #[derive(Debug, Serialize, ToSchema)]
 pub struct WebPubManifest {
     pub context: String,
@@ -26,6 +27,7 @@ pub struct WebPubManifest {
 }
 
 /// Metadata section of the WebPub Manifest
+#[allow(dead_code)]
 #[derive(Debug, Serialize, ToSchema)]
 pub struct WebPubMetadata {
     pub identifier: String,
@@ -44,6 +46,7 @@ pub struct WebPubMetadata {
 }
 
 /// Rendition properties for EPUB layout
+#[allow(dead_code)]
 #[derive(Debug, Serialize, ToSchema)]
 pub struct WebPubRendition {
     pub layout: String,