Reflow code comments to the 120-character line width

[d3mlabs-ai-flow]

From review discussion on #133: when we widened the Ruby line width from 80 to 120 (rubocop-shopify Layout/LineLength Max: 120), we never reflowed existing code comments — most are still wrapped at ~80 columns. New comments should fill the 120 width (as fixed in #133 for bin/release.rb), and the legacy ones should be swept.

Scope:

• Reflow comment blocks across src/, lib/, test/, and bin/ to fill up to 120 characters.
• Pure formatting: no wording changes, so review stays mechanical.
• One sweep PR (or a few per-directory ones) to keep blame noise contained.