Derive nav active state from the URL instead of passing an `active` prop

Each route renders `` and hand-passes its own identity (`graph-explorer`, `data-explorer`, `schema-explorer`, `connections`, `settings`) across 5 call sites. The nav bar already knows every route's path, so active state should derive from the current URL rather than being threaded in by each page.

Replace the `active` prop with React Router's `` / `useMatch` so `RouteButton` computes its own active state. `SettingsRoot` already uses `NavLink` this way — this brings the main nav in line.

**Affected files:** `components/RouteButton.tsx`, and the 5 call sites: `routes/GraphExplorer/GraphExplorer.tsx`, `routes/DataExplorer/DataExplorer.tsx`, `routes/SchemaExplorer/SchemaExplorer.tsx`, `routes/Connections/Connections.tsx`, `routes/Settings/SettingsRoot.tsx`.

**Outcome:** `active` prop and all 5 arguments removed; active styling driven by `NavLink` `isActive` / `useMatch`. No user-facing behavior change.

> [!IMPORTANT]
> Internal only — this issue is maintained by the core team and is not accepting external contributions.

Start with components/RouteButton.tsx and compare its current active prop handling with the NavLink usage in routes/Settings/SettingsRoot.tsx. Review the five listed route call sites, then verify that the active prop and five arguments are removed and that active styling is driven by the URL without changing user-facing behavior.

Written by the indexing model from the issue text.