feat: spin 백엔드 전체 구현 (근무·프로젝트·인센티브·회계)

- config/db/storage/auth/router/perms: eQMS 규약 미러링, 권한 2-tier
  (관리자 전체 / 구성원 본인·신청만), oauth2-proxy 헤더 인증 + DEV_AUTH mock
- 모델: 구성원/부서, 근무(출퇴근·휴가·공가·초과), 프로젝트(회사/제품/버전·
  작업자portion·담당자·태스크·계약·첨부·분할입금), 인센티브(설정·단계·
  유저배분·분기정산), 회계(거래·세금)
- internal/worktime: 근로기준법 월 집계 엔진
- internal/incentive: BE/non-BE × 계약금/중도금/잔금 3단계 계산 + 시뮬레이션
- 시드 데이터, Go 멀티스테이지 Dockerfile
- ADMIN_GROUPS 기본값 'admin' (전 내부 앱 공통 그룹)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/worktime/worktime.go

@@ -0,0 +1,78 @@
+// Package worktime computes monthly working-time roll-ups under the Korean Labor
+// Standards Act model: a 주 소정근로시간 (default 40h) baseline, business-day
+// expansion for the month, plus recognized leave/overtime.
+package worktime
+
+import "time"
+
+// MonthBusinessDays returns the count of weekdays (Mon–Fri) in the given month.
+// Public holidays are out of scope here; admins can adjust via leave/공가.
+func MonthBusinessDays(year int, month time.Month) int {
+	n := 0
+	d := time.Date(year, month, 1, 0, 0, 0, 0, time.UTC)
+	for d.Month() == month {
+		if wd := d.Weekday(); wd != time.Saturday && wd != time.Sunday {
+			n++
+		}
+		d = d.AddDate(0, 0, 1)
+	}
+	return n
+}
+
+// StandardMinutes is the expected worked minutes for the month: business days ×
+// the policy's daily standard minutes.
+func StandardMinutes(year int, month time.Month, dailyStandardMin int) int {
+	if dailyStandardMin <= 0 {
+		dailyStandardMin = 480
+	}
+	return MonthBusinessDays(year, month) * dailyStandardMin
+}
+
+// NetWorkMinutes computes worked minutes between clock-in and clock-out minus an
+// unpaid break. Returns 0 if either bound is missing or the span is negative.
+func NetWorkMinutes(in, out *time.Time, lunchMinutes int) int {
+	if in == nil || out == nil {
+		return 0
+	}
+	mins := int(out.Sub(*in).Minutes()) - lunchMinutes
+	if mins < 0 {
+		return 0
+	}
+	return mins
+}
+
+// Summary is the monthly timesheet roll-up returned to the UI.
+type Summary struct {
+	Year             int     `json:"year"`
+	Month            int     `json:"month"`
+	BusinessDays     int     `json:"businessDays"`
+	StandardMinutes  int     `json:"standardMinutes"`
+	WorkedMinutes    int     `json:"workedMinutes"`
+	LeaveMinutes     int     `json:"leaveMinutes"`     // recognized (연차/공가 등) as worked-equivalent
+	OvertimeMinutes  int     `json:"overtimeMinutes"`  // approved overtime
+	RecognizedTotal  int     `json:"recognizedTotal"`  // worked + leave
+	FulfillmentPct   float64 `json:"fulfillmentPct"`   // recognizedTotal / standard
+	DaysPresent      int     `json:"daysPresent"`
+}
+
+// Compute assembles the summary from raw minute inputs.
+func Compute(year, month, dailyStandardMin, worked, leave, overtime, daysPresent int) Summary {
+	std := StandardMinutes(year, time.Month(month), dailyStandardMin)
+	recognized := worked + leave
+	pct := 0.0
+	if std > 0 {
+		pct = float64(recognized) / float64(std) * 100
+	}
+	return Summary{
+		Year:            year,
+		Month:           month,
+		BusinessDays:    MonthBusinessDays(year, time.Month(month)),
+		StandardMinutes: std,
+		WorkedMinutes:   worked,
+		LeaveMinutes:    leave,
+		OvertimeMinutes: overtime,
+		RecognizedTotal: recognized,
+		FulfillmentPct:  pct,
+		DaysPresent:     daysPresent,
+	}
+}