Add pagination support to GET /api/v1/habits endpoint

- Create pagination package with Params and Response structs
- Add FindActiveByUserIDWithPagination and CountActiveByUserID methods to HabitRepository interface
- Implement pagination in SQLite repository using LIMIT and OFFSET
- Update GetUserHabitsHandler to support optional pagination parameters
- Modify HTTP endpoint to parse 'page' and 'page_size' query params (default: page=1, page_size=50, max=100)
- Add GetUserHabitsResponse DTO with pagination metadata
- Maintain backward compatibility - endpoint works with and without pagination params
- Add comprehensive tests for pagination logic in repository, handler, and pagination package
- Update all mock repositories to implement new pagination methods

internal/shared/pagination/pagination.go

@@ -0,0 +1,54 @@
+package pagination
+
+type Params struct {
+	Page     int
+	PageSize int
+}
+
+func NewParams(page, pageSize int) Params {
+	if page < 1 {
+		page = 1
+	}
+	if pageSize < 1 {
+		pageSize = 50
+	}
+	if pageSize > 100 {
+		pageSize = 100
+	}
+	return Params{
+		Page:     page,
+		PageSize: pageSize,
+	}
+}
+
+func (p Params) Offset() int {
+	return (p.Page - 1) * p.PageSize
+}
+
+func (p Params) Limit() int {
+	return p.PageSize
+}
+
+type Response struct {
+	Page       int `json:"page"`
+	PageSize   int `json:"page_size"`
+	TotalItems int `json:"total_items"`
+	TotalPages int `json:"total_pages"`
+}
+
+func NewResponse(params Params, totalItems int) Response {
+	totalPages := totalItems / params.PageSize
+	if totalItems%params.PageSize > 0 {
+		totalPages++
+	}
+	if totalPages < 1 {
+		totalPages = 1
+	}
+
+	return Response{
+		Page:       params.Page,
+		PageSize:   params.PageSize,
+		TotalItems: totalItems,
+		TotalPages: totalPages,
+	}
+}