fix(ui): 拖动松手从手指位置平滑契合到目标 tab

- 拖动状态与位置状态分离
- 松手先恢复过渡但保留手指位置，下一帧再吸附到目标 tab，避免从旧位置跳变

tools/custom-tab-bar.test.mjs

@@ -1,7 +1,12 @@
 import test from 'node:test'
 import assert from 'node:assert/strict'
+import { readFileSync } from 'node:fs'
+import { fileURLToPath } from 'node:url'
+import path from 'node:path'
 import { clampPercent, getTabBarFrame, hasDragged, tabIndexAtPercent } from '../src/custom-tab-bar/tabBarGeometry.js'
 
+const root = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..')
+
 test('maps a drag percent to the tab under the finger', () => {
   assert.equal(tabIndexAtPercent(10, 5), 0)
   assert.equal(tabIndexAtPercent(30, 5), 1)
@@ -28,3 +33,11 @@ test('derives the floating bar frame from window width', () => {
   assert.deepEqual(getTabBarFrame(375), { left: 18, width: 339 })
   assert.deepEqual(getTabBarFrame(750), { left: 36, width: 678 })
 })
+
+test('enables the slide transition before snapping the indicator to the target', () => {
+  const source = readFileSync(path.join(root, 'src/custom-tab-bar/index.tsx'), 'utf8')
+  assert.match(
+    source,
+    /isDraggingRef\.current = false\s+setIsDragging\(false\)\s+Taro\.nextTick\(\(\) => \{[\s\S]*?setDragPercent\(null\)/
+  )
+})