site: rename "finds" superpost collection to "bundles"

Disambiguates the one-letter `find` (item) vs `finds` (roundup) split that
kept causing confusion. Audience-facing now: `/bundles/<slug>/`, "Bundle"
labels in home/footer/search.

Internals: `getCollection('finds')` → `('bundles')`, `Entry.type 'finds'`
→ `'bundle'`, `OgFallback 'finds'` → `'bundles'`, `findListMosaic` →
`bundleMosaic`, `FindsPost` → `Bundle`, `findsReferencing` →
`bundlesReferencing`. Build script + generated mosaic dir follow
(`scripts/build-bundle-mosaics.mjs`, `src/generated/bundle-mosaics/`).

Skills `build-finds` → `build-bundle`, `cluster-finds` →
`cluster-bundles`. The `find` collection (individual items) is unchanged.

No URL redirects: low external-link surface area.

src/lib/seo.ts

@@ -1,13 +1,13 @@
 import { heroes } from './hero';
 import type { OgImage } from '../components/SEO.astro';
 
-export type OgFallback = 'reviews' | 'finds' | 'posts' | 'site';
+export type OgFallback = 'reviews' | 'bundles' | 'posts' | 'site';
 
 const SITE_URL = 'https://unique.rzen.dev';
 
 const FALLBACK_PATHS: Record<OgFallback, string> = {
   reviews: '/og/reviews.png',
-  finds: '/og/finds.png',
+  bundles: '/og/bundles.png',
   posts: '/og/posts.png',
   site: '/og/default.png',
 };