refactor: ES6+ modernization + 2 bugfixes

- var→const/let, function→arrow/class across all 13 JS files
- Timer: prototype→class with ES6 getters
- plan days: IIFE→Array.from declarative generation
- storage/plan: unified formatDate via util.js
- Bugfix: getPlanDay now filters by planId (plan switch accuracy)
- Bugfix: getTodayRecord searches all months (cross-month boundary)
- WXML/WXSS unchanged; public API unchanged

components/progress-ring/progress-ring.js

@@ -1,4 +1,4 @@
-var util = require('../../utils/util')
+const util = require('../../utils/util')
 
 Component({
   properties: {
@@ -17,8 +17,8 @@ Component({
   },
 
   observers: {
-    'remaining, status, duration, size, ringWidth, primaryColor': function () {
-      var texts = { idle: '准备开始', running: '坚持住', paused: '已暂停', completed: '完成!' }
+    'remaining, status, duration, size, ringWidth, primaryColor'() {
+      const texts = { idle: '准备开始', running: '坚持住', paused: '已暂停', completed: '完成!' }
       this.setData({
         displayTime: util.formatTime(this.data.remaining),
         statusText: texts[this.data.status] || ''
@@ -28,45 +28,40 @@ Component({
   },
 
   lifetimes: {
-    ready: function () {
-      var self = this
-      var query = this.createSelectorQuery()
+    ready() {
+      const query = this.createSelectorQuery()
       query.select('#ringCanvas')
         .fields({ node: true, size: true })
-        .exec(function (res) {
+        .exec((res) => {
           if (!res || !res[0] || !res[0].node) return
-          var canvas = res[0].node
-          var dpr = wx.getSystemInfoSync().pixelRatio || 2
-          var displaySize = self.data.size
+          const canvas = res[0].node
+          const dpr = wx.getSystemInfoSync().pixelRatio || 2
+          const displaySize = this.data.size
           canvas.width = displaySize * dpr
           canvas.height = displaySize * dpr
-          self._ctx = canvas.getContext('2d')
-          self._dpr = dpr
-          self._draw()
+          this._ctx = canvas.getContext('2d')
+          this._dpr = dpr
+          this._draw()
         })
     }
   },
 
   methods: {
-    _draw: function () {
-      var ctx = this._ctx
+    _draw() {
+      const ctx = this._ctx
       if (!ctx) return
 
-      var size = this.data.size
-      var dpr = this._dpr
-      var ringWidth = this.data.ringWidth
-      var duration = this.data.duration
-      var remaining = this.data.remaining
-      var primaryColor = this.data.primaryColor
+      const { size, ringWidth, duration, remaining, primaryColor } = this.data
+      const dpr = this._dpr
 
-      var w = size * dpr
-      var h = size * dpr
+      const w = size * dpr
+      const h = size * dpr
       ctx.clearRect(0, 0, w, h)
 
-      var cx = w / 2
-      var cy = h / 2
-      var radius = (size - ringWidth) / 2 * dpr
-      var lw = ringWidth * dpr
+      const cx = w / 2
+      const cy = h / 2
+      const radius = (size - ringWidth) / 2 * dpr
+      const lw = ringWidth * dpr
 
       // track ring
       ctx.beginPath()
@@ -76,11 +71,11 @@ Component({
       ctx.lineCap = 'round'
       ctx.stroke()
 
-      // progress arc (clockwise from 12 o'clock, represents remaining time)
-      var ratio = duration > 0 ? Math.max(0, Math.min(1, remaining / duration)) : 0
+      // progress arc (clockwise from 12 o'clock)
+      const ratio = duration > 0 ? Math.max(0, Math.min(1, remaining / duration)) : 0
       if (ratio > 0.001) {
-        var startAngle = -Math.PI / 2
-        var endAngle = startAngle + ratio * Math.PI * 2
+        const startAngle = -Math.PI / 2
+        const endAngle = startAngle + ratio * Math.PI * 2
         ctx.beginPath()
         ctx.arc(cx, cy, radius, startAngle, endAngle)
         ctx.strokeStyle = primaryColor