bring all views into conformance with the updated layout.md spec

[dprodger]

we made changes to SongDetailView including increasing the padding size to 24pt;

I want to roll those changes through everything.

[dprodger]

Done for iOS. The spacing scale is codified on ApproachNoteTheme (spacingXXS…spacingXL, doc/design/layout.md) and adopted across all iOS + Shared views; off-scale content gaps were reconciled to the scale.

Commits:

• a72a94e — add spacing tokens + adopt in SongDetailView (template) + doc update
• 2e79bee — adopt tokens across 39 iOS + Shared view/component files (value-preserving)
• 282e5e1 — snap off-scale content gaps (2→XXS, 6→XS, 10→XS)
• 230cb2c — snap remaining preview-only literals in ApproachNoteTheme

Remaining work split into follow-ups:

• Adopt spacing tokens across Mac views (follow-up to #199) #201 — adopt spacing tokens across Mac views
• Evaluate intentionally-left off-scale spacing values (bucket B & C) #202 — evaluate intentionally-left off-scale values (badge/pill insets, button/header/indent metrics, large page-level spacing)