feat(launcher): add display mode toggle; fix silent display layout failures

- Add Extend/Mirror toggle to Native OS config section (always visible,
  no Technical Mode required). Default: Extend. State updates on success.
- Replace .catch(() => {}) swallowing with console.warn logging on both
  set_display_layout call sites so failures appear in the Electron console
- Remove old edit-mode-only Extend button (replaced by new toggle)
- Update PROJECT doc: displayplacer install note, binary lookup order, GitHub link
- Clean up TODO__Agents.md: resolve stale items, add new low-priority Electron items

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

src/routes/events/[event_id]/(launcher)/cfg_components/launcher_cfg_native_os.svelte

@@ -6,6 +6,7 @@ import Launcher_Cfg_Section from './launcher_cfg_section.svelte';
 import {
     Code,
     Columns2,
+    Copy,
     FlaskConical,
     FolderOpen,
     Image,
@@ -27,6 +28,7 @@ let test_cmd_result = $state('');
 let remote_app: 'powerpoint' | 'keynote' = $state('powerpoint');
 let remote_status = $state('');
 let system_status = $state('');
+let display_mode = $state<'extend' | 'mirror'>('extend');
 
 async function handle_remote_control(
     action: 'next' | 'prev' | 'start' | 'stop'
@@ -55,6 +57,18 @@ async function handle_system_action(promise: Promise<any>, label: string) {
     setTimeout(() => (system_status = ''), 3000);
 }
 
+async function handle_display_mode(mode: 'extend' | 'mirror') {
+    system_status = `Setting display: ${mode}...`;
+    const res = await native.set_display_layout({ mode });
+    if (res?.success) {
+        display_mode = mode;
+        system_status = `Display: ${mode}`;
+    } else {
+        system_status = `Display error: ${res?.error || 'No external display?'}`;
+    }
+    setTimeout(() => (system_status = ''), 4000);
+}
+
 // Modal state for dangerous actions
 let show_power_confirm = $state<{ action: string; label: string } | null>(null);
 </script>
@@ -124,6 +138,33 @@ let show_power_confirm = $state<{ action: string; label: string } | null>(null);
         </div>
     </div>
 
+    <!-- Display mode toggle: Extend = independent screens (default); Mirror = same content on both -->
+    <div class="flex flex-col gap-2">
+        <p class="ml-1 text-[9px] font-bold uppercase opacity-50">Display Mode</p>
+        <div class="grid grid-cols-2 gap-1">
+            <button
+                type="button"
+                onclick={() => handle_display_mode('extend')}
+                class="btn btn-xs justify-start border-2"
+                class:border-primary-500={display_mode === 'extend'}
+                class:preset-tonal-primary={display_mode === 'extend'}
+                class:border-surface-400={display_mode !== 'extend'}
+                class:preset-tonal-surface={display_mode !== 'extend'}>
+                <Columns2 size="0.85em" class="mr-1 shrink-0" /> Extend
+            </button>
+            <button
+                type="button"
+                onclick={() => handle_display_mode('mirror')}
+                class="btn btn-xs justify-start border-2"
+                class:border-warning-500={display_mode === 'mirror'}
+                class:preset-tonal-warning={display_mode === 'mirror'}
+                class:border-surface-400={display_mode !== 'mirror'}
+                class:preset-tonal-surface={display_mode !== 'mirror'}>
+                <Copy size="0.85em" class="mr-1 shrink-0" /> Mirror
+            </button>
+        </div>
+    </div>
+
     <!-- 2. Presentation Remote Control (Common) -->
     <div class="flex flex-col gap-2">
         <div class="flex flex-row items-center justify-between px-1">
@@ -186,19 +227,6 @@ let show_power_confirm = $state<{ action: string; label: string } | null>(null);
                         System Actions
                     </p>
                     <div class="grid grid-cols-1 gap-1">
-                        <button
-                            type="button"
-                            onclick={() =>
-                                handle_system_action(
-                                    native.set_display_layout({
-                                        mode: 'extend'
-                                    }),
-                                    'Extend Display'
-                                )}
-                            class="btn btn-xs preset-tonal-surface hover:preset-filled-primary-500 justify-start">
-                            <Columns2 size="0.85em" class="mr-1 shrink-0" /> Extend
-                            Mode
-                        </button>
                         <button
                             type="button"
                             onclick={() =>

src/routes/events/[event_id]/(launcher)/launcher_file_cont.svelte

@@ -219,9 +219,8 @@ async function handle_open_file() {
         // URL presentations may still want to set display mode (e.g. Google Slides → extend)
         if (profile.display_mode !== 'none') {
             open_file_status_message = `Setting display (${profile.display_mode})...`;
-            await native.set_display_layout({ mode: profile.display_mode }).catch(() => {
-                /* No external display or displayplacer unconfigured — continue */
-            });
+            const disp_res = await native.set_display_layout({ mode: profile.display_mode }).catch((e: any) => ({ success: false, error: String(e) }));
+            if (!disp_res?.success) console.warn('[Launcher] set_display_layout:', disp_res?.error ?? 'no external display');
         }
 
         open_file_status_message = `Opening ${event_file_obj.title || 'URL'}...`;
@@ -357,9 +356,8 @@ async function handle_open_file() {
         // --- Step 3: Set display layout (skip silently on failure / no external display) ---
         if (profile.display_mode !== 'none') {
             open_file_status_message = `Setting display (${profile.display_mode})...`;
-            await native.set_display_layout({ mode: profile.display_mode }).catch(() => {
-                /* No external display or displayplacer unavailable — continue */
-            });
+            const disp_res = await native.set_display_layout({ mode: profile.display_mode }).catch((e: any) => ({ success: false, error: String(e) }));
+            if (!disp_res?.success) console.warn('[Launcher] set_display_layout:', disp_res?.error ?? 'no external display');
         }
 
         // --- Step 4: Open the file ---