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-core/src/capture.rs

@@ -78,10 +78,9 @@ impl PlatformMetadata {
 pub struct CaptureConfig {
     pub cookie_rules: Vec<database::CookieRule>,
     /// Override for uBlock Origin Lite during WebPage captures.
-    /// `None` = derive from `ARCHIVR_UBLOCK` env var (existing behaviour).
-    /// `Some(false)` = disabled by admin/user choice for this capture.
-    /// `Some(true)` = explicitly enabled (still needs `ARCHIVR_UBLOCK_EXT` to be valid).
     pub ublock_enabled: Option<bool>,
+    /// Apply Mozilla Readability to distil the page to article content before archiving.
+    pub reader_mode: bool,
 }
 
 /// Resolves which cookies apply to `url` by evaluating all rules in ordinal order.
@@ -1015,7 +1014,7 @@ pub fn perform_capture(
 
     // Source: web page — archive as a self-contained HTML snapshot via single-file-cli
     if source == Source::WebPage {
-        match downloader::singlefile::save(locator, store_path, &timestamp, &cookies, config.ublock_enabled) {
+        match downloader::singlefile::save(locator, store_path, &timestamp, &cookies, config.ublock_enabled, config.reader_mode) {
             Ok(result) => {
                 let file_extension = ".html".to_string();
                 let temp_html = store_path