Add CSV export of scan results

The Review tab gets an Export CSV menu: "This view" exports the current
status filter and search, "Entire scan" exports every scanned slave file.

Each row carries status, match type, a recommendation, slave/master paths,
the link target, the match reason, sizes, codec details for both sides,
the quality verdict, notes, errors and timestamps. Rows are streamed in
pages of 1000 so a large export never holds the database connection a
running scan needs. The file starts with a UTF-8 BOM for Excel, and cells
a spreadsheet would evaluate as formulas are prefixed with an apostrophe.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -57,6 +57,11 @@ codec-weighted bitrate (Opus and AAC count for more per kbps than MP3). You then
   libraries share the better file.
 - **Ignore.** The pair is hidden from review until you un-ignore it.
 
+**Export.** The Review tab's **Export CSV** button downloads either the current view (filter and search applied) or the entire scan.
+Each row has the match status and type, a recommendation, both paths, where linking would place the file, codec, bitrate, sample rate,
+bit depth and duration for both sides, the quality verdict and any notes. The file opens cleanly in Excel, Numbers and LibreOffice
+(UTF-8, and cells a spreadsheet would treat as formulas are escaped).
+
 **Build mode** covers the "start fresh" workflow. Point the slave at an empty folder, browse the master library, tick the
 folders or songs you want, and playlink hardlinks them in at the same relative path. **Remove** deletes slave files, but only ones that are hardlinks of the
 master file.