feat(tabs): drag-reorder + double-click rename + per-tab chat draft

- TabBar: HTML5 drag-and-drop to reorder user tabs (subagent tabs untouched);
  double-click a tab title to rename (Enter/blur confirm, Escape cancel).
- Store: add reorderTabs/renameTab/setDraft; per-tab in-memory `draft` and
  `manualTitle` fields. Manual rename suppresses first-message auto-title.
- ChatInput: bind to the active tab's draft so switching tabs saves/restores
  unsent text instead of clobbering it.
- Backend: updateTabPositions() + PATCH /tabs/reorder persist tab order to the
  existing `position` column; tabs without a stored position fall to the end
  then get explicit positions on first reorder.
- Tests: store reorder/rename/auto-title-guard/draft coverage; core
  updateTabPositions coverage (FakeDatabase extended with transaction support).

2 files changed, 15 insertions, 0 deletions

diff --git a/packages/core/src/db/tabs.ts b/packages/core/src/db/tabs.ts
index 8b290d2..f719a01 100644
--- a/packages/core/src/db/tabs.ts
+++ b/packages/core/src/db/tabs.ts
@@ -115,6 +115,20 @@ export function updateTabStatus(id: string, status: string): void {
 	});
 }
 
+export function updateTabPositions(idsInOrder: string[]): void {
+	const db = getDatabase();
+	const now = Date.now();
+	const update = db.query("UPDATE tabs SET position = $position, updated_at = $now WHERE id = $id");
+	// One transaction so a reorder is atomic: either every tab lands at its new
+	// slot or none does, never a half-applied ordering.
+	const applyAll = db.transaction(() => {
+		idsInOrder.forEach((id, index) => {
+			update.run({ $id: id, $position: index, $now: now });
+		});
+	});
+	applyAll();
+}
+
 export function archiveTab(id: string): void {
 	const db = getDatabase();
 	db.query("UPDATE tabs SET is_open = 0, updated_at = $now WHERE id = $id").run({
diff --git a/packages/core/src/index.ts b/packages/core/src/index.ts
index 7818024..f67ad53 100644
--- a/packages/core/src/index.ts
+++ b/packages/core/src/index.ts
@@ -56,6 +56,7 @@ export {
 	shortestUniquePrefix,
 	type TabRow,
 	updateTabModel,
+	updateTabPositions,
 	updateTabStatus,
 	updateTabTitle,
 } from "./db/tabs.js";