feat(ext/popup): add pop-out to tab for forms

Forms can now be opened in a full browser tab via the ⤴ button,
solving Chrome's popup closure on file picker interaction. Deep
linking via URL params preserves view, item type, and item ID.

Also removes the unused dropdown picker code from item-list.ts.

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

extension/src/popup/components/item-form.ts

@@ -1,7 +1,7 @@
 /// Typed-item add/edit form dispatcher. Each type's renderForm lives in
 /// its own module under ./types/. Document stays "coming soon" until γ.
 
-import { navigate, getState, setState, escapeHtml } from '../popup';
+import { navigate, getState, setState, escapeHtml, popOutToTab } from '../popup';
 import type { Item, ItemType } from '../../shared/types';
 
 const TYPE_OPTIONS: Array<{ type: ItemType; icon: string; label: string }> = [
@@ -57,6 +57,8 @@ function renderTypeSelection(app: HTMLElement): void {
       <div style="display:flex; align-items:center; gap:12px; margin-bottom:16px;">
         <button class="btn" id="back-btn">← back</button>
         <h3 style="margin:0;">new item</h3>
+        <span style="flex:1;"></span>
+        <button class="btn" id="popout-btn" title="Open in tab">⤴</button>
       </div>
       <div class="type-select-list">
         ${TYPE_OPTIONS.map((opt) => `
@@ -70,6 +72,7 @@ function renderTypeSelection(app: HTMLElement): void {
   `;
 
   document.getElementById('back-btn')?.addEventListener('click', () => navigate('list'));
+  document.getElementById('popout-btn')?.addEventListener('click', popOutToTab);
 
   document.querySelectorAll<HTMLButtonElement>('[data-type]').forEach((btn) => {
     btn.addEventListener('click', () => {