feat(i18n): full app + docs localization (de/en)

- translate remaining pages/components (admin, analytics, redundancy,
  trash, compare, browse, watchlist, admin tools tab, category combobox,
  theme toggle, tool preview card, tool-new/edit) to t() calls
- locales: 453 keys each, parity verified
- docs: bilingual handbook + release notes via *.en.md variants,
  language-aware docs.tsx (markdown paths, nav titles, search index),
  LanguageSwitcher in docs header
- generate-docs: emit per-locale handbook/release/search output,
  localized index.json fields (fileEn/titleEn), en-aware snapshots

docs/releases/v0.8.1/handbook/kosten.en.md

@@ -0,0 +1,35 @@
+
+# Recording Costs
+
+On the detail page of a tool you can enter cost and license models so that
+the total costs per tool become transparent.
+
+> Costs is a **premium feature** (`costs`, Premium/Enterprise). Admins always
+> have access.
+
+## Adding costs
+
+Click **Add costs** in the costs section of the detail page and fill out the
+form:
+
+| Field | Notes |
+| --- | --- |
+| **License type** | Free / Subscription / One-Time / Usage-Based |
+| **Billing period** | Only for "Subscription": Monthly / Quarterly / Annually |
+| **Costs** | Amount as a number |
+| **Currency** | EUR / USD / GBP / CHF |
+| **Notes** | Optional free text |
+
+Saving creates the entry. Each cost entry is displayed as a card with
+license badge, billing period, amount (`Amount Currency` or "Free") and
+notes.
+
+## Editing & deleting costs
+
+Hovering over a cost card shows the **Edit** (pencil) and **Delete** (trash)
+actions.
+
+## API
+
+The cost data is managed via the tool endpoints
+(see [API reference](/docs/reference/endpoints/tools)).