feat: focus item detail page with inline note + checklist

Each standalone focus item now auto-creates a linked note and checklist.
Clicking a focus item opens a detail page with side-by-side note editor
(left) and checklist (right) with drag-to-reorder. Save & Return writes
the note and goes back to the focus list. Added focus_id FK to notes and
lists tables, made domain optional when creating from focus context.

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

templates/focus_edit.html

@@ -3,7 +3,9 @@
 <div class="breadcrumb">
     <a href="/focus">Focus</a>
     <span class="sep">/</span>
-    <span>Edit Item</span>
+    <a href="/focus/{{ item.id }}">{{ item.title or 'Item' }}</a>
+    <span class="sep">/</span>
+    <span>Edit</span>
 </div>
 
 <div class="page-header">
@@ -45,7 +47,7 @@
 
             <div class="form-actions">
                 <button type="submit" class="btn btn-primary">Save Changes</button>
-                <a href="/focus" class="btn btn-secondary">Cancel</a>
+                <a href="/focus/{{ item.id }}" class="btn btn-secondary">Cancel</a>
             </div>
         </div>
     </form>