feat: crawler scaffold with chromium launcher (0.22.0)

- crawler module (browser, source trait, jobs, diff) + binary
- chromiumoxide launcher with fetcher feature (auto-downloads
  Chromium on first run, caches under ~/.cache/mangalord/chromium)
- LaunchOptions struct with extra_args, parseable from
  CRAWLER_BROWSER_MODE and CRAWLER_BROWSER_ARGS
- migration 0012 introduces sources, manga_sources,
  chapter_sources, crawler_jobs
- integration tests for headed + headless launch, ipify load+parse,
  and extra-args propagation (all #[ignore], opt-in)

backend/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.21.3"
+version = "0.22.0"
 edition = "2021"
 
 [lib]
@@ -10,6 +10,10 @@ path = "src/lib.rs"
 name = "mangalord"
 path = "src/main.rs"
 
+[[bin]]
+name = "crawler"
+path = "src/bin/crawler.rs"
+
 [dependencies]
 axum = { version = "0.7", features = ["macros", "multipart"] }
 tokio = { version = "1", features = ["full"] }
@@ -36,7 +40,10 @@ time = "0.3"
 infer = "0.16"
 tokio-util = { version = "0.7", features = ["io"] }
 futures-core = "0.3"
+futures-util = "0.3"
 bytes = "1"
+chromiumoxide = { version = "0.7", features = ["tokio-runtime", "_fetcher-rusttls-tokio"], default-features = false }
+scraper = "0.20"
 
 [dev-dependencies]
 tempfile = "3"