feat(gui): paste button, Enter-to-connect, version, and clipboard prefill

Quick viewer-flow polish:

- a "📋 Paste" button pinned to the right of the code field — the read-side
  mirror of the host's Copy button;
- Enter in the code field connects (same decode gate as the button);
- the View screen prefills the field from the clipboard on open when it holds
  a decodable ticket and the field is empty, so the freshly-shared code is
  usually already there (live decode still shows the id to verify);
- the menu shows the binary version under the heading.

Tightens the common "host clicks Copy → viewer clicks Paste → Connect" loop;
the prefill only ever drops in a *valid* ticket, so it can't reintroduce the
stale/garbage paste it guards against.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/gui/mod.rs

@@ -43,6 +43,15 @@ fn set_clipboard(text: &str) -> bool {
         .is_ok()
 }
 
+/// Best-effort clipboard read, backing the viewer Paste button and the
+/// View-screen prefill. `None` on a flaky/empty clipboard — callers just leave
+/// the field untouched.
+fn get_clipboard() -> Option<String> {
+    arboard::Clipboard::new()
+        .and_then(|mut cb| cb.get_text())
+        .ok()
+}
+
 /// Decode the host endpoint id from a ticket string, using the exact same
 /// parse the viewer does (`EndpointTicket::from_str`), so the GUI agrees with
 /// the child about what's a valid code. `None` means it isn't a pixelpass
@@ -233,6 +242,11 @@ impl PixelPassApp {
             ui.add_space(24.0);
             ui.heading("PixelPass");
             ui.label("P2P screen sharing");
+            ui.label(
+                egui::RichText::new(concat!("v", env!("CARGO_PKG_VERSION")))
+                    .small()
+                    .weak(),
+            );
             ui.add_space(32.0);
             if ui
                 .add_sized([260.0, 40.0], egui::Button::new("Host — share my screen"))
@@ -249,6 +263,7 @@ impl PixelPassApp {
                 .clicked()
             {
                 self.screen = Screen::Viewer;
+                self.prefill_viewer_ticket();
             }
         });
     }
@@ -580,11 +595,26 @@ impl PixelPassApp {
 
         ui.label("Paste the share code you received:");
         ui.add_space(4.0);
-        ui.add(
-            egui::TextEdit::singleline(&mut self.viewer.ticket_input)
-                .desired_width(f32::INFINITY)
-                .hint_text("endpoint…"),
-        );
+        // Field fills the row, with a Paste button pinned to its right — the
+        // read-side mirror of the host's Copy button (one click grabs the code
+        // the host just put on the clipboard).
+        let ticket_resp = ui
+            .with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
+                if ui.button("📋 Paste").clicked()
+                    && let Some(text) = get_clipboard()
+                {
+                    self.viewer.ticket_input = text.trim().to_string();
+                }
+                ui.add(
+                    egui::TextEdit::singleline(&mut self.viewer.ticket_input)
+                        .desired_width(f32::INFINITY)
+                        .hint_text("endpoint…"),
+                )
+            })
+            .inner;
+        // Enter in the field connects (gated on a decodable code below).
+        let enter_pressed =
+            ticket_resp.lost_focus() && ui.input(|i| i.key_pressed(egui::Key::Enter));
 
         // Decode the pasted code live: confirms it's a real ticket and shows
         // which host it points at, so a stale clipboard paste is caught here
@@ -621,14 +651,14 @@ impl PixelPassApp {
 
         ui.add_space(16.0);
         // Only dial a code that actually decodes — no point spawning a child to
-        // spend 15s timing out against garbage.
-        if ui
+        // spend 15s timing out against garbage. Enter takes the same path.
+        let connect_clicked = ui
             .add_enabled(
                 decoded_id.is_some(),
                 egui::Button::new("Connect").min_size(egui::vec2(140.0, 36.0)),
             )
-            .clicked()
-        {
+            .clicked();
+        if decoded_id.is_some() && (connect_clicked || enter_pressed) {
             self.start_viewer(ui.ctx().clone());
         }
     }
@@ -656,6 +686,22 @@ impl PixelPassApp {
         }
     }
 
+    /// On entering the View screen, drop a clipboard ticket straight into the
+    /// field — the host's Copy button (and our auto-copy) usually leaves the
+    /// freshly-shared code right there. Guarded so it only fires when the field
+    /// is empty and the clipboard holds a *decodable* ticket, so stray
+    /// clipboard text never lands in the box; the live decode still shows the
+    /// id for the user to verify.
+    fn prefill_viewer_ticket(&mut self) {
+        if self.viewer.ticket_input.trim().is_empty()
+            && self.viewer.proc.is_none()
+            && let Some(text) = get_clipboard()
+            && ticket_endpoint_id(&text).is_some()
+        {
+            self.viewer.ticket_input = text.trim().to_string();
+        }
+    }
+
     fn start_viewer(&mut self, ctx: egui::Context) {
         self.viewer.error = None;
         self.viewer.url = None;