feat: add cumulative checkin tracking mode for goals

Goals can now choose between milestone-based progress (existing) and
cumulative checkin-based progress (new). Cumulative mode supports
cross-unit conversion (e.g. kcal → g fat) via a configurable
conversion rate. New GoalCheckin model stores daily inputs; progress
auto-recalculates on every checkin C/U/D. Backup import/export covers
the new table. Frontend GoalDialog, GoalDetailPage and GoalPage cards
adapt to show cumulative progress or milestone progress based on
track_type.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

api/app/routers/backup.py

@@ -18,14 +18,14 @@ EXPORT_TABLES = [
     "categories", "tags", "user_settings", "sync_settings",
     "habit_groups", "anniversary_categories", "certificate_categories",
     "goals", "tasks", "habits", "anniversaries", "certificates",
-    "goal_steps", "goal_reviews", "habit_checkins",
+    "goal_steps", "goal_reviews", "goal_checkins", "habit_checkins",
     "task_tags", "goal_tasks",
 ]
 
 # 导入时的清表顺序：子表先删（避免 FK 约束报错）
 TRUNCATE_ORDER = [
     "task_tags", "goal_tasks",
-    "habit_checkins",
+    "habit_checkins", "goal_checkins",
     "goal_reviews", "goal_steps",
     "tasks", "habits", "anniversaries", "certificates",
     "goals", "categories", "tags",
@@ -38,7 +38,7 @@ INSERT_ORDER = [
     "categories", "tags", "user_settings", "sync_settings",
     "habit_groups", "anniversary_categories", "certificate_categories",
     "goals", "tasks", "habits", "anniversaries", "certificates",
-    "goal_steps", "goal_reviews", "habit_checkins",
+    "goal_steps", "goal_reviews", "goal_checkins", "habit_checkins",
     "task_tags", "goal_tasks",
 ]