Replace free-text genre field with structured style dropdowns

The customer request form previously had an open 'Style / genre / mood'
text field, which produced inconsistent genre descriptions and confused
Suno. Replace it with three dropdowns:

- Decade / era (required) — loaded from /mnt/Storage/Decades.txt
- Basic style (required) — loaded from /mnt/Storage/Music Genres.txt
- Additional style (optional) — same genre list

The combined value is stored in the existing style_genre column as a
comma-separated string (e.g. '1980's, Pop, Funk'), so no schema change
is required. The admin request page exposes the same dropdowns for
corrections, and the copy-to-Hermes prompt formats the style as a clean
sentence like '1980's-era Pop with Funk influences'.

The canonical lists live in /mnt/Storage; bundled copies under lists/
act as a fallback when that mount is unavailable in the container.

Bumps version to 0.4.6 and updates README.

lists/decades.txt

@@ -0,0 +1,10 @@
+Early 20th Centrury
+1940's
+1950's
+1960's
+1970's
+1980's
+1990's
+2000's
+2010's
+Modern