Add Mortgage Refinancing Calculator (v3) to the framework

[jenbreese]

NOT READY FOR REVIEW

Summary

Incorporates the standalone v0/shadcn Mortgage Refinancing Calculator (v3) into this repo as a normal route so it can be reviewed and iterated on in-framework. This is a lift-and-fit only — the calculator's math and display are unchanged from the original. It's a starting point for deciding what to adapt to our conventions (Stanford tokens, shared UI components, validation rules, etc.), not a finished calculator.

What changed

New route (app/interactives/mortgage-refinancing-calculator-v3/)

• page.tsx — the route: loads the original Geist fonts, renders the original header + , wrapped in a .mortgage-refi-v3 scope.

• components/refinance-calculator.tsx — the calculator component, brought over as-is (only the broken import path fixed).

• lib/mortgage.ts — the present-value / amortization helpers, unchanged.

• theme.css — the v3 palette (light, class-dark, and system-preference dark), scoped to .mortgage-refi-v3 so it reproduces the original look without touching the Stanford tokens every other calculator uses.

• globals.css — an unscoped reference copy of the original theme, kept for review (not imported by the build).

• Shared theme (app/ui/globals.css)

• Registered three color tokens in @theme that the calculator needs (--color-panel, --color-panel-foreground, --color-navy-foreground).

• Moved brand navy behind a --navy variable (was an inlined literal) so it resolves identically for every existing bg-navy/text-navy while being overridable by scoped themes. All additive and behavior-preserving for other calculators.

Cleanup

• Removed the standalone app scaffolding that would break the build: nested app/, package.json, pnpm-lock.yaml, next.config.mjs, postcss.config.mjs, components.json, tsconfig.json, .gitignore, and the unused components/ui/button.tsx / lib/utils.ts.
• Fixed the one broken import (@/lib/mortgage → ../lib/mortgage).
• Removed two pieces of dead code from the original that blocked us: an undefined setNewAmountTouched() call that crashed "Reset new loan terms," and an unused closingCosts prop that failed lint. Neither affects any calculation or displayed value.

Verification

• yarn lint — passes (only a pre-existing warning in an unrelated file).
• yarn build:local — succeeds; the route statically exports alongside all others.
• yarn dev — route serves 200, renders correctly, dark mode and Reset both work.
• Not in scope (follow-ups to review)
• Still uses the original v0 palette/components rather than our shared shadcn primitives, InfoPopover, ThemeToggle, and Stanford tokens.
• Does not yet follow our validation conventions (invalid-input-stays-visible, "Please enter…" messages, error/warning states, result suppression).
• Math has not been re-derived/audited against our standards yet.