feat(root-cms): replace preact-router with preact-iso for routing

[stevenle]

Motivation

• Migrate the root-cms UI to use preact-iso instead of preact-router to align with the project's current routing/hooks API and remove the ad-hoc type shim.
• Update navigation usages to the useLocation hook and the preact-iso Router/Route exports so routing data and navigation are accessed via the new API.

Description

• Replaced preact-router Route/Router imports with preact-iso in the app shell (packages/root-cms/ui/ui.tsx).
• Swapped usages of route/useRouter to the useLocation hook from preact-iso and adjusted call sites to read url or route from useLocation() in multiple components including Layout, CollectionPage, NewDocModal, CopyDocModal, DataSourceForm, ReleaseForm, DocEditor, EditDataSourcePage, and EditReleasePage.
• Updated packages/root-cms/package.json to replace the preact-router dependency with preact-iso and removed the custom preact-router.d.ts shim file.
• Minor callback dependency update in DocEditor to include the route reference where appropriate to keep hooks stable.

Testing

• No automated tests were run for this change (per project instructions).

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Codex Task