# Regression: `/categories` must not render campaign edit

## Symptom (fixed)
Nav/URL on **Categories** (`/categories`) sometimes showed **Edit campaign** chrome with a blank body.

## Cause notes
- Route files are distinct: `routes/categories/+page.svelte` vs `routes/campaigns/[id]/+page.svelte`.
- SvelteKit dictionary maps `/categories` → categories page and `/campaigns/[id]` → campaign edit.
- Campaign edit previously rendered `PageShell` titled "Edit campaign" even when `page.params.id` was empty (blank body) — that shell must never linger across client navigations.

## Guards added
1. Root dashboard layout keys page content by `page.url.pathname` so prior route shells unmount on nav.
2. Campaign edit redirects to `/campaigns` when `id` is missing; wizard is keyed by `campaignId`.

## Quick check
1. Open `/campaigns/<any-id>` (or list), then click **Categories** in the nav.
2. Assert H1 is **Categories** and body shows the category tree (not "Edit campaign").
3. Hard-load `/categories` — same result.