fix: reminder_time format for habits and tasks (HH:MM instead of timestamp)

internal/model/habit.go

@@ -2,6 +2,7 @@ package model
 
 import (
 	"database/sql"
+	"strings"
 	"time"
 )
 
@@ -12,8 +13,8 @@ type Habit struct {
 	Description     string         `db:"description" json:"description"`
 	Color           string         `db:"color" json:"color"`
 	Icon            string         `db:"icon" json:"icon"`
-	Frequency       string         `db:"frequency" json:"frequency"` // daily, weekly, custom
-	TargetDays      []int          `db:"-" json:"target_days"`       // 0=Sun, 1=Mon, etc.
+	Frequency       string         `db:"frequency" json:"frequency"`
+	TargetDays      []int          `db:"-" json:"target_days"`
 	TargetCount     int            `db:"target_count" json:"target_count"`
 	ReminderTime    sql.NullString `db:"reminder_time" json:"-"`
 	ReminderTimeStr *string        `db:"-" json:"reminder_time"`
@@ -23,8 +24,23 @@ type Habit struct {
 }
 
 func (h *Habit) ProcessForJSON() {
-	if h.ReminderTime.Valid {
-		h.ReminderTimeStr = &h.ReminderTime.String
+	if h.ReminderTime.Valid && h.ReminderTime.String != "" {
+		timeStr := h.ReminderTime.String
+		// Handle formats like "0000-01-01T19:00:00Z" or "19:00:00"
+		if strings.Contains(timeStr, "T") {
+			// Parse as timestamp and extract time
+			t, err := time.Parse(time.RFC3339, timeStr)
+			if err == nil {
+				formatted := t.Format("15:04")
+				h.ReminderTimeStr = &formatted
+				return
+			}
+		}
+		// Handle "19:00:00" format
+		if len(timeStr) >= 5 {
+			formatted := timeStr[:5]
+			h.ReminderTimeStr = &formatted
+		}
 	}
 }
 
@@ -62,7 +78,7 @@ type UpdateHabitRequest struct {
 }
 
 type LogHabitRequest struct {
-	Date  string `json:"date,omitempty"` // YYYY-MM-DD, defaults to today
+	Date  string `json:"date,omitempty"`
 	Count int    `json:"count,omitempty"`
 	Note  string `json:"note,omitempty"`
 }