feat: default crawler browser to headless (0.32.0)

LaunchOptions::from_env() and LaunchOptions::default() now return
BrowserMode::Headless. The in-process daemon (via CrawlerConfig::from_env)
and the standalone crawler binary both pick this up — no display
required for production runs, smaller resource footprint.

`Headed` stays as an explicit opt-in via CRAWLER_BROWSER_MODE=headed
for debugging or sites that fingerprint headless Chrome. New unit test
locks the default in place.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/Cargo.lock

@@ -1470,7 +1470,7 @@ checksum = "c41e0c4fef86961ac6d6f8a82609f55f31b05e4fce149ac5710e439df7619ba4"
 
 [[package]]
 name = "mangalord"
-version = "0.31.0"
+version = "0.32.0"
 dependencies = [
  "anyhow",
  "argon2",

backend/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.31.0"
+version = "0.32.0"
 edition = "2021"
 default-run = "mangalord"
 

backend/src/crawler/browser.rs

@@ -27,12 +27,12 @@ use tokio::task::JoinHandle;
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum BrowserMode {
     /// Real window. Needs `$DISPLAY` (or `xvfb-run` wrapping the
-    /// binary). This is the default the old Puppeteer crawler used and
-    /// the assumed mode for the target site until we prove headless
-    /// works against it.
+    /// binary). Opt-in via `CRAWLER_BROWSER_MODE=headed` — useful for
+    /// debugging a flow visually or for sites that fingerprint
+    /// headless Chrome. Not used in production.
     Headed,
-    /// No window. Faster, lower resource use, but more likely to trip
-    /// fingerprinting on hostile sites.
+    /// No window. Faster, lower resource use, runs without a display.
+    /// This is the default for both `from_env()` and `Default`.
     Headless,
 }
 
@@ -65,13 +65,13 @@ impl LaunchOptions {
     }
 
     /// Reads `CRAWLER_BROWSER_MODE` (`headless`|`headed`, default
-    /// `headed`) and `CRAWLER_BROWSER_ARGS` (whitespace-separated
+    /// `headless`) and `CRAWLER_BROWSER_ARGS` (whitespace-separated
     /// Chromium flags). Flags containing whitespace aren't supported
     /// through the env var — use the programmatic API for those.
     pub fn from_env() -> Self {
         let mode = match std::env::var("CRAWLER_BROWSER_MODE").as_deref() {
-            Ok("headless") => BrowserMode::Headless,
-            _ => BrowserMode::Headed,
+            Ok("headed") => BrowserMode::Headed,
+            _ => BrowserMode::Headless,
         };
         let extra_args = std::env::var("CRAWLER_BROWSER_ARGS")
             .map(|s| parse_args(&s))
@@ -82,7 +82,7 @@ impl LaunchOptions {
 
 impl Default for LaunchOptions {
     fn default() -> Self {
-        Self::headed()
+        Self::headless()
     }
 }
 
@@ -251,4 +251,14 @@ mod tests {
         assert!(parse_args("").is_empty());
         assert!(parse_args("   \t\n").is_empty());
     }
+
+    #[test]
+    fn default_launch_options_are_headless() {
+        // Headless is the production-safe default — no display required,
+        // smaller resource footprint. `Headed` stays available as an
+        // opt-in for debugging via CRAWLER_BROWSER_MODE=headed.
+        assert_eq!(LaunchOptions::default().mode, BrowserMode::Headless);
+        assert_eq!(LaunchOptions::headless().mode, BrowserMode::Headless);
+        assert_eq!(LaunchOptions::headed().mode, BrowserMode::Headed);
+    }
 }