Wire missing page routes and catch-all 404 (Closes #143)

[matthewrball]

Summary

• Wire built pages that existed but were unreachable: /campaigns, /campaigns/new, /investor (real InvestorDashboardPage), /farmer, /profile.
• Keep /dashboard/* aliases so older header hrefs still resolve.
• Put /campaigns/new before /campaigns/:id so new is not treated as an id.
• Catch-all * renders the existing NotFoundPage instead of a blank unmatched route.
• Point primary nav at the new paths (plus a Create-campaign link).

Closes #143

Notes

• HomePage from pages/index.tsx stays unrouted on purpose; / remains DesignFoundationsPage.
• Farmer/campaigns list pages are still the placeholders exported from pages/index.tsx — this PR only makes them reachable.
• GrantFox Third Campaign / Maybe Rewarded (not escrowed).

Test plan

• /campaigns shows the campaigns placeholder and Create link
• /campaigns/new renders CreateCampaignPage
• /campaigns/some-id still renders CampaignDetailPage
• /investor renders the real investor dashboard (not the index placeholder)
• /farmer and /profile render their placeholders
• Unknown path (e.g. /nope) shows NotFoundPage
• Header nav links hit those routes
• client/: npm run lint, npm test