Chore / Spike: Upgrade app to rails 7.2

[ChargrilledChook]

Quick spike to test effort of ugprading to Rails 7.2, as there aren't many huge changes.

Findings: low effort.

Notes:

• Linters failing in CI but not locally via bin/test, likely because CI uses rubocop binstub and new config adds an explicit .rubocop.yml load
• Defaults recommend changing the default max thread count from 5 to 3
• Check if YJIT is in the Docker image we use
• Some ActiveJob weirdness in console when running app locally, but could just be janky state in local env.
• Several Rails 8 deprecations notices being spammed, particularly for enums - see change here

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This commit:

• Update version in Gemfile
• Run bundle update
• Run app:update task
• Fix broken specs
• Toggle new framework defaults