feat(rain): add date preset picker and reduce time clarification prompts.

Default to last 3 days in UI and backend, only ask when time is truly ambiguous, and treat「做成页面」as HTML report pages without follow-up questions.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/utils/rainTimeRange.ts

@@ -0,0 +1,12 @@
+export type RainTimePresetId = 'today' | 'yesterday' | '3d' | '7d';
+
+export const RAIN_SKILL_ID = 'rain';
+
+export const RAIN_TIME_PRESET_OPTIONS: ReadonlyArray<{ id: RainTimePresetId; label: string }> = [
+  { id: 'today', label: '今天' },
+  { id: 'yesterday', label: '昨天' },
+  { id: '3d', label: '近3天' },
+  { id: '7d', label: '近7天' },
+];
+
+export const DEFAULT_RAIN_TIME_PRESET: RainTimePresetId = '3d';