feat: crawler manga-list & metadata sync with cover download (0.23.0)

- TargetSource: first concrete impl of the Source trait, modeled on
  the old Puppeteer crawler's selectors (+ status normalization,
  tag-count stripping, chapter list)
- DiscoverMode::Backfill walks pagination last->1, reverse within each
  page (oldest-first); Incremental walks forward
- RateLimiter (tokio-time aware) plumbed through FetchContext so the
  pagination walk honors the same per-host budget as the outer loop
- repo::crawler: ensure_source, upsert_manga_from_source (returns
  New/Updated/Unchanged + current cover_image_path for backfill
  decisions), sync_manga_chapters, mark_dropped_mangas — all
  transactional, with case-insensitive lookups and source-insertable
  genres
- Cover image download via reqwest+infer; stored under
  mangas/{id}/cover.{ext} via the Storage trait
- Single CRAWLER_PROXY env wires both Chromium (--proxy-server) and
  reqwest::Proxy::all (HTTP/HTTPS/SOCKS5)
- Crawler binary: positional start URL or $CRAWLER_START_URL,
  $CRAWLER_LIMIT (cap fetches + skip drop pass on partial runs),
  $CRAWLER_SKIP_CHAPTERS (disable selector AND sync), $CRAWLER_RATE_MS
- Silences chromiumoxide 0.7's known CDP deserialize log spam via
  default tracing filter + CdpError::Serde downgrade
- 9 sqlx integration tests + 11 selector/rate-limit unit tests

backend/src/crawler/browser.rs

@@ -18,6 +18,7 @@ use std::path::PathBuf;
 
 use anyhow::Context;
 use chromiumoxide::browser::{Browser, BrowserConfig};
+use chromiumoxide::error::CdpError;
 use chromiumoxide::fetcher::{BrowserFetcher, BrowserFetcherOptions};
 use futures_util::StreamExt;
 use tokio::task::JoinHandle;
@@ -169,8 +170,16 @@ pub async fn launch(options: LaunchOptions) -> anyhow::Result<Handle> {
 
     let driver = tokio::spawn(async move {
         while let Some(event) = handler.next().await {
-            if let Err(err) = event {
-                tracing::warn!(?err, "chromium handler event error");
+            match event {
+                Ok(_) => {}
+                // chromiumoxide 0.7 ships fixed CDP type bindings, so any
+                // CDP event Chrome added later fails to deserialize. The
+                // connection is unaffected — these are noise. Suppress
+                // them so real failures stay visible.
+                Err(CdpError::Serde(_)) => {
+                    tracing::trace!("chromium emitted an unrecognized CDP event");
+                }
+                Err(err) => tracing::warn!(?err, "chromium handler event error"),
             }
         }
     });