refactor: einheitliche .chip-Klasse für Filter-Chips, .btn-outline.btn-sm für Adressbuch-Actions

- app.css: neue .chip Utility (rounded-xs, border, text-[11px])
- AdressbuchBlock: Org-/Letter-Filter auf .chip, Action-Buttons auf .btn-outline.btn-sm
- CalendarBlock: Tag-Filter auf .chip

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/components/blocks/CalendarBlock.svelte

@@ -925,7 +925,7 @@
             <button
                 type="button"
                 onclick={() => (activeTag = null)}
-                class="text-[11px] px-2 py-0.5 rounded-xs border {!activeTag
+                class="chip {!activeTag
                     ? 'bg-himmel-700 text-himmel-50 border-himmel-700'
                     : 'border-stein-300 text-stein-700 hover:bg-stein-100'}"
                 aria-pressed={!activeTag}
@@ -936,8 +936,7 @@
                 <button
                     type="button"
                     onclick={() => (activeTag = activeTag === tag ? null : tag)}
-                    class="text-[11px] px-2 py-0.5 rounded-xs border {activeTag ===
-                    tag
+                    class="chip {activeTag === tag
                         ? 'bg-himmel-700 text-himmel-50 border-himmel-700'
                         : 'border-stein-300 text-stein-700 hover:bg-stein-100'}"
                     aria-pressed={activeTag === tag}