tauri-app: 8c profile copy buttons

The profile view now has two clipboard actions:
  * 'copy did'  — copies the bare DID to the system clipboard
  * 'copy at-uri' — copies 'at://<did>/app.twi.post' as a shareable link

Both surface a toast confirmation via the existing
maarcadetweet:notification event, so the user gets a small
'copied: ...' toast for confirmation. Right-click on a toast
still dismisses without action.

The copyToClipboard helper is in App.svelte (not pushed to
client.ts) because it only uses the browser navigator API.

crates/tauri-app/src/App.svelte

@@ -135,6 +135,25 @@
     }
   }
 
+  async function copyToClipboard(text: string) {
+    try {
+      await navigator.clipboard.writeText(text);
+      // Surface a tiny inline confirmation by reusing the toast stack.
+      // We dispatch the toast event (not pushToast directly) so the
+      // notification toast gets the close-on-click behavior.
+      const ev = new CustomEvent("maarcadetweet:notification", {
+        detail: {
+          title: "clipboard",
+          body: `copied: ${text.length > 40 ? text.slice(0, 37) + "…" : text}`,
+          url: null,
+        },
+      });
+      window.dispatchEvent(ev);
+    } catch (e) {
+      pushToast("error", `> clipboard failed: ${String(e)}`);
+    }
+  }
+
   // We need to hoist these into the onMount closure (which is below)
   // so the addEventListener / removeEventListener pair stays paired.
   // (`_toastHandler` is the function below; the other two are
@@ -425,6 +444,21 @@
                 <span class="profile__handle">{displayHandle(profile.handle)}</span>
                 <span class="profile__did" title={profile.did}>{profile.did}</span>
               </header>
+              <div class="profile__actions">
+                <button
+                  class="btn btn--ghost"
+                  type="button"
+                  title="Copy DID to clipboard"
+                  onclick={() => copyToClipboard(profile!.did)}
+                >copy did</button>
+                <button
+                  class="btn btn--ghost"
+                  type="button"
+                  title="Copy AT URI to clipboard"
+                  onclick={() =>
+                    copyToClipboard(`at://${profile!.did}/app.twi.post`)}
+                >copy at-uri</button>
+              </div>
               <dl class="counts">
                 <div>
                   <dt>followers</dt>
@@ -540,6 +574,12 @@
     overflow: auto;
     padding: var(--s-3);
   }
+
+  .profile__actions {
+    display: flex;
+    gap: var(--s-2);
+    margin: var(--s-3) 0;
+  }
   .head {
     font-family: var(--font-mono);
     font-size: var(--fs-50);