Add KiDerivation modal for Competitive Binding module

[meganrm]

Problem

Estimated review size: medium

KiQuestion's failure message told students to "Visit the 'Learn how to derive Ki' button above," but no such button or modal existed anywhere in the Competitive Binding module — unlike KdQuestion's equivalent message, which correctly points at a real KdDerivation modal in the High Affinity module.

Fixes #227

Solution

Built a KiDerivation modal (and KiDerivationContent) mirroring KdDerivation's existing pattern, and wired it onto the same content page as the KiQuestion quiz — the same placement pattern KdDerivation uses. Content is adapted/condensed from the module's existing "Deriving Ki" page rather than written from scratch. KiQuestion.tsx's failure message text is unchanged — it was already correct copy, it just had nothing to point to.

⚠️ This adds new derivation-explainer content — please review for accuracy against the existing "Deriving Ki" page it's adapted from.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Change summary:

• New KiDerivation/KiDerivationContent components mirroring KdDerivation/KdDerivationContent
• Wired the modal onto the existing "Deriving Ki" content page in Competitive.tsx

Steps to Verify:

1. Reach the Ki quiz question in the Competitive Binding module
2. Click the "Learn how to derive Ki" button — confirm the modal opens and steps through correctly
3. Answer the quiz incorrectly — confirm the failure message now points at a working button
4. Compare the modal's content against the existing "Deriving Ki" page for fidelity

Screenshots (optional):

Keyfiles (delete if not relevant):

1. src/components/modals/KiDerivation.tsx
2. src/components/modals/KiDerivationContent.tsx
3. src/content/Competitive.tsx

Thanks for contributing!