feat: compare limit 9, format-aware import placeholder, help links

- Raise compare limit from 8 to 9 (server + client, toast on overflow)
- Make import textarea placeholder match selected format (CSV/JSON/YAML/auto)
- Add GuideHelp links to admin create/edit user dialogs and tool import dialog

docs/releases/v0.9.1/handbook/vergleichen.en.md

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+
+# Compare
+
+With the compare function you can put several tools **side by side** —
+ideal for making a well-informed decision.
+
+> Comparing is a **premium feature** (Premium/Enterprise) and is always
+> available to admins.
+
+## Selecting tools
+
+1. In the **Browse tools** section, click the **compare icon** (scales) on
+   each card/row.
+2. The **compare bar** appears at the bottom with the selected tools as
+   chips. You can remove individual tools (×) or clear the selection.
+3. Click **Compare (N)** to go to the compare view.
+
+> Without a premium plan the button is locked (lock icon). The dialog takes
+> you to the plan switch
+> (see [Plans & permissions](/docs/handbook/plaene)).
+
+## The compare view
+
+The view shows a table with one column per tool. Rows:
+
+| Row | Content |
+| --- | --- |
+| **Rating** | Stars + value (e.g. `4.2/5`) |
+| **Usefulness** | Value (X.X/5) |
+| **Usability** | Value (X.X/5) |
+| **Number of ratings** | Count |
+| **Description** | Text |
+| **Features** | Badges |
+| **Tags** | Badges |
+| **Last updated** | Date |
+
+The **best value** per row is highlighted (with trophy icon).
+
+## API
+
+The compare view reads the data via
+[`GET /compare`](/docs/reference/endpoints/tools#listCompareTools).