Make wikilink relations visible: what links here, and which linked pages
do not exist yet.
- shared: `BacklinkView` gains a plain-text `snippet` for context.
- api: `LinksService` includes a short snippet (from the content cache) with
each backlink and phantom referrer.
- web:
- `BacklinksPanel` below a page in read mode: a collapsible "Linked from"
list (title + snippet, links to the source), hidden when empty. Appears
on load from the #47 index.
- `PhantomPagesView` in pond settings: wikilink targets that do not exist
yet, each with its referrers and a create shortcut that makes the page
under the phantom slug — resolving those links (#47) and navigating to it.
- i18n `links` namespace (de + en); backlinks + missing-pages styles.
- e2e `backlinks.spec.ts` (new CI pack): a link created in the editor appears
as a backlink on the target; the missing-pages view lists a phantom slug and
creating it navigates to the new page.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PGdhRiwU1WRL4XxJfZYipY
