fix: prevent scanner from recreating renamed series

When a user renames a series via the UI, the scanner was using the
filesystem directory name to overwrite the DB series name, effectively
undoing the rename. This adds an original_name column to series_metadata
that tracks the filesystem-derived name, so the scanner can map it back
to the user-chosen name. The migration also back-fills existing renamed
series by comparing book file paths with DB series names.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

infra/migrations/0062_add_series_original_name.sql

@@ -0,0 +1,32 @@
+-- Track the filesystem-derived series name so the scanner can map
+-- renamed series back to their current DB name.
+-- When a user renames series "A" → "B", original_name stores "A" (the directory name).
+ALTER TABLE series_metadata ADD COLUMN original_name TEXT;
+
+-- Back-fill original_name for series that were already renamed:
+-- compare the DB series name with the actual directory name from book_files.abs_path.
+-- If they differ, the series was renamed and we record the filesystem name.
+UPDATE series_metadata sm
+SET original_name = fs.fs_series
+FROM (
+    SELECT DISTINCT ON (b.library_id, b.series)
+        b.library_id,
+        b.series,
+        -- First path component after the library root = filesystem series name
+        split_part(
+            ltrim(
+                replace(bf.abs_path, l.root_path, ''),
+                '/'
+            ),
+            '/',
+            1
+        ) AS fs_series
+    FROM books b
+    JOIN book_files bf ON bf.book_id = b.id
+    JOIN libraries l ON l.id = b.library_id
+    WHERE b.series IS NOT NULL AND b.series != ''
+) fs
+WHERE sm.library_id = fs.library_id
+  AND sm.name = fs.series
+  AND fs.fs_series != ''
+  AND fs.fs_series != fs.series;