feat(tags): moderators and admins can delete public tags

Add DELETE /api/tags/:name (gated by isModerator(), which also passes
for admins per the admin-implies-moderator invariant in roles.ts).
The endpoint normalises the name the same way creation does so the
URL casing doesn't matter, then deletes the tag and detaches it from
every activity_tags row in one transaction.

UI: new "Etiketter" nav entry visible to moderators + admins, opens
a ModerateTags.svelte view with search-as-you-type (reusing the
/api/tags suggestion endpoint) and a Slett button per row. Private
tags are unaffected — they're encrypted in the activity payload and
never reach the server tag table.

Tests: 3 new cases on top of the admin suite — moderator can delete,
plain user gets 403 (anonymous gets 401), unknown tag gets 404.

frontend/src/App.svelte

@@ -12,6 +12,7 @@
   import Feedback from './components/Feedback.svelte';
   import PublicList from './components/PublicList.svelte';
   import Admin from './components/Admin.svelte';
+  import ModerateTags from './components/ModerateTags.svelte';
   import ActivityPermalink from './components/ActivityPermalink.svelte';
   import Personvern from './components/Personvern.svelte';
   import TagPage from './components/TagPage.svelte';
@@ -34,7 +35,7 @@
     | 'login' | 'signup' | 'recovery'
     | 'public-home'     // "/" — public/semi only, anyone
     | 'home'            // "/home" — full authenticated dashboard
-    | 'profile' | 'feedback' | 'admin'
+    | 'profile' | 'feedback' | 'admin' | 'moderate-tags'
     | 'public-list'     // "/<username>/list"
     | 'permalink'       // "/a/:id"
     | 'personvern'      // "/personvern"
@@ -210,6 +211,12 @@
           {#if session.user.is_admin}
             <button type="button" onclick={() => (view = 'admin')}>Admin</button>
           {/if}
+          {#if session.user.is_moderator || session.user.is_admin}
+            <button type="button" onclick={() => (view = 'moderate-tags')}
+                    aria-label="Moderer etiketter">
+              Etiketter
+            </button>
+          {/if}
           <button type="button" onclick={() => (view = 'feedback')}
                   aria-label="Send tilbakemelding">
             Tilbakemelding
@@ -258,6 +265,8 @@
     <Feedback onDone={goHome} />
   {:else if view === 'admin'}
     <Admin onDone={goHome} />
+  {:else if view === 'moderate-tags'}
+    <ModerateTags onDone={goHome} />
   {:else if view === 'personvern'}
     <Personvern onBack={leavePersonvern} />
   {:else if view === 'tag'}

frontend/src/components/ModerateTags.svelte

@@ -0,0 +1,124 @@
+<script lang="ts">
+  import { onMount } from 'svelte';
+  import { api, ApiError } from '../lib/api';
+  import type { TagSuggestion } from '../../../shared/types';
+
+  interface Props {
+    onDone: () => void;
+  }
+  let { onDone }: Props = $props();
+
+  let tags: TagSuggestion[] = $state([]);
+  let query = $state('');
+  let loading = $state(true);
+  let error: string | null = $state(null);
+  let busy: Record<string, boolean> = $state({});
+
+  onMount(() => load(''));
+
+  // Reload from the server whenever the search query changes. The endpoint
+  // is paginated at 50 — moderators search to narrow large tag sets rather
+  // than scrolling a single dump. Same behaviour as TagInput's suggestion fetch.
+  $effect(() => {
+    const q = query;
+    const timer = setTimeout(() => load(q), 150);
+    return () => clearTimeout(timer);
+  });
+
+  async function load(q: string) {
+    loading = true;
+    error = null;
+    try {
+      tags = await api.tagSuggestions(q, 50);
+    } catch (err) {
+      error = err instanceof ApiError && err.status === 403
+        ? 'Bare moderatorer kan se denne siden.'
+        : 'Kunne ikke laste etiketter.';
+    } finally {
+      loading = false;
+    }
+  }
+
+  async function remove(name: string) {
+    if (!confirm(`Slett etiketten «${name}» fra alle aktiviteter?`)) return;
+    busy = { ...busy, [name]: true };
+    try {
+      await api.deleteTag(name);
+      tags = tags.filter((t) => t.name !== name);
+    } catch (err) {
+      error = err instanceof ApiError && err.status === 403
+        ? 'Du har ikke rettigheter til å slette etiketter.'
+        : 'Sletting feilet.';
+    } finally {
+      const { [name]: _, ...rest } = busy;
+      busy = rest;
+    }
+  }
+</script>
+
+<section aria-label="Moderer etiketter">
+  <div class="row" style="justify-content: space-between; margin-bottom: 1rem;">
+    <h2 style="margin: 0;">Moderer etiketter</h2>
+    <button type="button" onclick={onDone}>Tilbake</button>
+  </div>
+
+  <p class="muted">
+    Sletting fjerner etiketten fra alle offentlige, anonyme og vennlige
+    aktiviteter den finnes på. Private etiketter er kryptert og ikke
+    synlige her.
+  </p>
+
+  <label for="tag-search" style="margin-top: 1rem;">Søk</label>
+  <input
+    id="tag-search"
+    type="search"
+    bind:value={query}
+    placeholder="Søk etter etikett …"
+    aria-label="Søk etter etikett"
+  />
+
+  {#if error}<p class="error" role="alert">{error}</p>{/if}
+
+  {#if loading}
+    <p class="muted">Laster …</p>
+  {:else if tags.length === 0}
+    <p class="muted">
+      {query ? `Ingen etiketter matcher «${query}».` : 'Ingen etiketter ennå.'}
+    </p>
+  {:else}
+    <div class="card" style="padding: 0; overflow-x: auto;">
+      <table style="width: 100%; border-collapse: collapse;">
+        <thead>
+          <tr style="border-bottom: 1px solid var(--border);">
+            <th scope="col" style="text-align: left; padding: 0.5rem;">Etikett</th>
+            <th scope="col" style="text-align: right; padding: 0.5rem;">Bruk</th>
+            <th scope="col" style="padding: 0.5rem;"></th>
+          </tr>
+        </thead>
+        <tbody>
+          {#each tags as t (t.name)}
+            <tr style="border-bottom: 1px solid var(--border);">
+              <td style="padding: 0.5rem;">
+                <span class="tag" style="font-size: inherit;">{t.name}</span>
+              </td>
+              <td style="padding: 0.5rem; text-align: right;" class="muted">
+                {t.usage_count}
+              </td>
+              <td style="padding: 0.5rem; text-align: right;">
+                <button
+                  class="danger"
+                  type="button"
+                  disabled={busy[t.name]}
+                  onclick={() => remove(t.name)}
+                  aria-label={`Slett etikett ${t.name}`}
+                >
+                  Slett
+                </button>
+              </td>
+            </tr>
+          {/each}
+        </tbody>
+      </table>
+    </div>
+  {/if}
+</section>

frontend/src/lib/api.ts

@@ -91,6 +91,10 @@ export const api = {
   // --- tags -----------------------------------------------------------------
   tagSuggestions: (q: string, limit = 20) =>
     http<TagSuggestion[]>(`/tags?q=${encodeURIComponent(q)}&limit=${limit}`),
+  // Moderator/admin: delete a public tag entirely (also detaches it from all
+  // activities). Forbidden for regular users.
+  deleteTag: (name: string) =>
+    http<void>(`/tags/${encodeURIComponent(name)}`, { method: 'DELETE' }),
 
   // --- users (opt-in public list) -------------------------------------------
   publicList: (username: string) =>