feat: Reader mode via Mozilla Readability.js

Adds an opt-in 'Reader mode' advanced option to the capture dialog.
When enabled, Readability.js is injected as a browser script during
SingleFile capture; it fires on single-file-on-before-capture-start,
replaces the page body with the distilled article content, injects a
clean typographic stylesheet, and adds a header with title/byline/site.
Falls back silently if Readability fails (e.g. non-article pages).

- vendor/readability/Readability.js  Apache 2.0, Mozilla, v0.6.0
- singlefile.rs: embed READABILITY_JS + READER_MODE_WRAPPER_JS via
  include_str!; write both to temp dir when reader_mode is true;
  base_single_file_cmd now accepts &[&Path] for multiple --browser-script
- capture.rs: CaptureConfig.reader_mode: bool
- routes.rs: CaptureBody.reader_mode: Option<bool> (defaults false)
- api.js: submitCapture passes reader_mode in payload
- CaptureDialog.jsx: Reader mode toggle in Advanced options (off by default)

crates/archivr-server/src/routes.rs

@@ -650,11 +650,10 @@ async fn delete_entry_handler(
 #[derive(Debug, serde::Deserialize)]
 struct CaptureBody {
     locator: String,
-    /// Optional quality cap for yt-dlp sources: `"best"` or any `"NNNp"` string
-    /// (e.g. `"1080p"`, `"720p"`, `"2160p"`). Absent or `"best"` → highest available.
     quality: Option<String>,
-    /// Per-capture uBlock override.  Absent → use global instance setting.
     ublock_enabled: Option<bool>,
+    /// Distil to article content via Readability before archiving.  Absent = false.
+    reader_mode: Option<bool>,
 }
 
 #[derive(Debug, serde::Deserialize)]
@@ -754,6 +753,7 @@ async fn capture_handler(
     let capture_config = capture::CaptureConfig {
         cookie_rules,
         ublock_enabled: Some(effective_ublock),
+        reader_mode: body.reader_mode.unwrap_or(false),
     };
 
     // Spawn background capture.