Add missing content to riffs

- add more chords like: D7(b9) and D9(#11) as chord and as scale with quarter notes
- add more scales en riffs that go down -> make it more symmetric by creating a "down" riff for all current "up" riffs

Start by locating the Python/Flask code that defines the current chords, scales, and riffs, then compare the existing up-riff data with the requested additions. Done means D7(b9) and D9(#11) are represented as chords and quarter-note scales, and corresponding down riffs exist for the current up riffs.

索引モデルが issue の本文から書いたものです。