[P1.1] Next.js 16 prep: useRouter().pathname → usePathname()

[frano-m]

Parent: #884 (Next.js 16 Upgrade Plan)

Scope

Migrate findable-ui call sites using useRouter().pathname (from next/router) to usePathname() (from next/navigation). Approximately 5 call sites.

Tasks

• Grep for useRouter().pathname and router.pathname patterns under src/.
• For each, replace with usePathname().
• Remove the now-unused useRouter import if no other router APIs are used in the file.
• Verify type signatures (usePathname() returns string | null — handle null where needed).
• Run npm run lint && npm test.

Acceptance

• All useRouter().pathname sites migrated.
• Tests pass.
• No behavior regression.

Part of #884.