feat(ui): copyable input partial + dynamic copy-target

- New core partial templates/partials/app-input-copy.phtml renders a
  standard label + input with a compact copy button overlaid on the
  right edge of the input. Used for privacy/imprint URLs on the tenant
  form; reusable for any field where a one-click copy is helpful.
- Extend the shared copy-field component (web/js/components/app-copy-field.js)
  with data-copy-target support — the button now reads the target input's
  .value at click-time, so users can edit a field and still copy the
  current value. Static data-copy-value keeps working unchanged.
- New component CSS web/css/components/app-input-copy.css positions the
  button absolute/inset + margin-block:auto (robust vertical centering
  regardless of input height) and uses a descendant selector (0,2,0)
  so the button wins over the global [data-tooltip] position:relative.
- Also register app-input-copy.css + app-tenant-logo.css in core.css
  @import list — they were only in the shared asset group before, which
  default-template admin pages don't load, so tenant-logo styles were
  effectively missing on admin tenant edit (topbar size etc.).
- Document the Copy-to-Clipboard + Copyable Input standards in
  docs/reference-frontend-javascript.md so future consumers don't
  re-invent the markup/selectors.
- File-upload preview: pending-file block restructured to a compact
  list-item row (small square thumb + filename/size stack + clear X)
  and removed the transparency checker pattern on the current-image
  preview in favour of a flat --app-preview-bg surface.
- Tenant edit page title + breadcrumb now show the tenant description
  ("Acme GmbH") instead of the generic "Mandant bearbeiten" when one
  is present.
- i18n: add "Copy to clipboard" / "In Zwischenablage kopieren" across
  both locales.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/reference-frontend-javascript.md

@@ -306,6 +306,85 @@ Für standardisierte Detailseiten gilt zusätzlich:
 - Aktionssemantik über `data-detail-action-kind` (z. B. `save`, `save-close`, `delete`, `danger`).
 - Optionaler Lock-Override über `data-detail-submit-lock="none"` (Default: `form`).
 
+### Copy-to-Clipboard Standard
+
+Für kopierbare Inhalte (Werte, Feld-Inhalte, Badges) gilt eine einzige
+Component: `web/js/components/app-copy-field.js` — ein Button mit
+`data-copy-button` bekommt automatisch einen Click-Handler, der in die
+Zwischenablage schreibt und 1,2 s lang ein Check-Icon statt des Copy-Icons
+anzeigt (Klasse `is-copied` wird am Button getoggelt).
+
+Zwei Quell-Modi:
+
+- **Statischer Wert** (fix im Markup):
+  ```html
+  <button type="button" data-copy-button data-copy-value="max@acme.com"
+          aria-label="Copy email">
+    <i class="bi bi-copy" data-copy-icon-idle></i>
+    <i class="bi bi-check-lg" data-copy-icon-done></i>
+  </button>
+  ```
+
+- **Live Input-Wert** (liest `input.value` beim Klick):
+  ```html
+  <input id="privacy_url" …>
+  <button type="button" data-copy-button data-copy-target="privacy_url" …>…</button>
+  ```
+  Der Live-Modus ist vorzuziehen, wenn der User das Feld editieren kann —
+  der Button kopiert dann immer den aktuellen Wert, nicht den beim ersten
+  Render gesetzten.
+
+### Copyable Input Standard
+
+Für Text-Inputs, bei denen ein Copy-Button *im* Feld sitzen soll (z. B. URLs,
+IDs, Tokens) existiert die Core-Partial **`templates/partials/app-input-copy.phtml`**.
+
+Verwendung im Form:
+
+```php
+<?php
+$name = 'privacy_url';
+$label = t('Privacy URL');
+$type = 'url';
+$value = (string) ($values['privacy_url'] ?? '');
+$readonly = $isReadOnly;
+require templatePath('partials/app-input-copy.phtml');
+?>
+```
+
+Optionale Vars: `$id` (Default = `$name`), `$placeholder`, `$required`,
+`$disabled`. Die Partial rendert:
+
+```html
+<label for="privacy_url">
+  <span>Privacy URL</span>
+  <div class="app-input-copy">
+    <input type="url" name="privacy_url" id="privacy_url" value="…">
+    <button class="app-input-copy-button" data-copy-button
+            data-copy-target="privacy_url" …>
+      <i class="bi bi-clipboard" data-copy-icon-idle></i>
+      <i class="bi bi-check-lg" data-copy-icon-done></i>
+    </button>
+  </div>
+</label>
+```
+
+CSS-Kontrakt (`web/css/components/app-input-copy.css`):
+
+- `.app-input-copy` — Positioning-Wrapper, `position: relative`
+- `.app-input-copy > input` — Native Form-Styling, `padding-right: 2.5rem`
+  für den Overlay-Button
+- `.app-input-copy > .app-input-copy-button` — absolute positioniert rechts,
+  vertikal zentriert via `inset 0/auto + margin-block: auto`. Spezifität
+  `(0,2,0)` beim Descendant-Selector nötig, damit die globale
+  `[data-tooltip] { position: relative }`-Regel nicht gewinnt.
+- `.is-copied` (wird vom Copy-Field-Component gesetzt) — tauscht Copy-Icon
+  gegen Check, färbt Button in `--app-action-success-border`.
+
+Nicht selbst die Markup-Struktur nachbauen — immer die Partial verwenden,
+damit Spacing, Vertical-Centering und A11y (`aria-label`, Tooltip) konsistent
+bleiben.
+
 ### Global Confirm Actions
 
 Für allgemeine Form-/Button-Confirms außerhalb der Detail-Policy gilt: