feat: 工资查询助手首版 v1.0.105

基于 skill-template 脚手架开发，包含：
- payroll_config（费率配置，可编辑）+ payslip_snapshots（解析历史，只读）2 张业务表
- 全国默认 + 北上广 4 套费率（社保/公积金/个税起征点/7 级税率表）
- 5 个业务 Action：calculate-payslip-simple / calculate-payslip-full / explain-term / view-config / edit-config
- 个税累计预扣法计算，支持多月历史累加
- 20 个薪资名词库（社保/公积金/个税/全勤/加班费等）
- 完整市场文档（README/TUTORIAL/DEMO/CHANGELOG）
- 296 测试全部通过

scripts/service/tax_service.py

@@ -0,0 +1,161 @@
+"""个税累计预扣计算服务。
+
+按"累计预扣法"计算当月个税：
+  累计预扣预缴应纳税所得额 = 累计收入 - 累计减除费用 - 累计专项扣除 - 累计专项附加扣除 - 累计依法确定的其他扣除
+  当月应预扣预缴税额 = (累计预扣预缴应纳税所得额 × 预扣率 - 速算扣除数) - 已预扣预缴税额
+
+简化假设：
+- 专项附加扣除与其他扣除暂不计入（数据不可得）
+- 累计减除费用 = 5000 × 当年至本月份数
+- 累计专项扣除 = 累计社保+公积金个人部分（从历史 snapshots 读取）
+"""
+
+from __future__ import annotations
+
+import time
+from typing import Any
+
+from service.config_service import get_config_value, get_tax_brackets
+from db.connection import get_conn
+from util.logging_config import get_skill_logger
+
+log = get_skill_logger()
+
+
+def _month_index(period: str) -> int:
+    """从 'YYYY-MM' 提取月份数（1-12）。"""
+    try:
+        return int(period.split("-")[1])
+    except (ValueError, IndexError):
+        return 1
+
+
+def _year_of_period(period: str) -> str:
+    """从 'YYYY-MM' 提取年份。"""
+    try:
+        return period.split("-")[0]
+    except (ValueError, IndexError):
+        return "1970"
+
+
+def get_cumulative_deduction_before(period: str) -> dict[str, float]:
+    """读取同一年的历史 snapshots，累计社保/公积金个人部分。
+
+    period 之前的同一年 snapshots（按 period 字符串排序 < 当前 period）。
+    返回 {social_cum, housing_fund_cum, tax_cum}。
+    """
+    year = _year_of_period(period)
+    conn = get_conn()
+    try:
+        cur = conn.cursor()
+        cur.execute(
+            """
+            SELECT detail_json FROM payslip_snapshots
+            WHERE period LIKE ? AND period < ?
+            ORDER BY period ASC
+            """,
+            (f"{year}-%", period),
+        )
+        import json
+        social_cum = 0.0
+        housing_fund_cum = 0.0
+        tax_cum = 0.0
+        for (detail_str,) in cur.fetchall():
+            if not detail_str:
+                continue
+            try:
+                detail = json.loads(detail_str)
+            except (json.JSONDecodeError, TypeError):
+                continue
+            ded = detail.get("deduction", {}) if isinstance(detail, dict) else {}
+            social_cum += float(ded.get("social", {}).get("personal_total", 0) or 0)
+            housing_fund_cum += float(ded.get("housing_fund", {}).get("personal", 0) or 0)
+            tax_cum += float(ded.get("tax", {}).get("actual", 0) or 0)
+        return {"social_cum": social_cum, "housing_fund_cum": housing_fund_cum, "tax_cum": tax_cum}
+    finally:
+        conn.close()
+
+
+def compute_cumulative_tax(
+    *,
+    current_gross: float,
+    period: str,
+    current_social: float,
+    current_housing_fund: float,
+    region: str = "default",
+) -> dict[str, Any]:
+    """按累计预扣法计算当月个税。
+
+    返回 {
+        actual_tax: float,       # 本次应预扣个税
+        cumulative_income: float,
+        cumulative_deduction: float,
+        cumulative_taxable: float,
+        cumulative_tax: float,   # 累计应预扣
+        prior_tax_paid: float,   # 之前已预扣
+        brackets_used: dict,     # 命中的税率档
+        has_history: bool,       # 是否有历史累计数据
+        note: str,
+    }
+    """
+    log.info(
+        "tax_compute_start period=%s gross=%s social=%s housing=%s region=%s",
+        period, current_gross, current_social, current_housing_fund, region,
+    )
+    threshold = get_config_value("tax_threshold", region) or 5000
+    brackets = get_tax_brackets(region)
+
+    month_idx = _month_index(period)
+    cumulative_threshold = float(threshold) * month_idx
+
+    prior = get_cumulative_deduction_before(period)
+    has_history = prior["social_cum"] > 0 or prior["tax_cum"] > 0
+
+    cumulative_income = current_gross + prior.get("income_cum", 0.0) if has_history else current_gross
+    # 简化：累计专项扣除 = 累计社保+公积金个人
+    cumulative_special_deduction = (
+        prior["social_cum"] + prior["housing_fund_cum"]
+        + current_social + current_housing_fund
+    )
+
+    cumulative_taxable = cumulative_income - cumulative_threshold - cumulative_special_deduction
+    if cumulative_taxable < 0:
+        cumulative_taxable = 0.0
+
+    cumulative_tax = 0.0
+    bracket_hit = None
+    if brackets and cumulative_taxable > 0:
+        for bracket in brackets:
+            upper = bracket.get("upper")
+            rate = float(bracket.get("rate", 0))
+            quick = float(bracket.get("quick_deduction", 0))
+            if upper is None or cumulative_taxable <= float(upper):
+                cumulative_tax = cumulative_taxable * rate - quick
+                bracket_hit = bracket
+                break
+        if bracket_hit is None and brackets:
+            bracket_hit = brackets[-1]
+            rate = float(bracket_hit.get("rate", 0))
+            quick = float(bracket_hit.get("quick_deduction", 0))
+            cumulative_tax = cumulative_taxable * rate - quick
+
+    cumulative_tax = max(0.0, cumulative_tax)
+    prior_tax_paid = prior["tax_cum"] if has_history else 0.0
+    actual_tax = max(0.0, cumulative_tax - prior_tax_paid)
+
+    note = "仅供参考，非官方数据"
+    if not has_history:
+        note = "仅供参考（无累计历史数据，累计按本月单月计算），非官方数据"
+
+    return {
+        "actual_tax": round(actual_tax, 2),
+        "cumulative_income": round(cumulative_income, 2),
+        "cumulative_threshold": round(cumulative_threshold, 2),
+        "cumulative_special_deduction": round(cumulative_special_deduction, 2),
+        "cumulative_taxable": round(cumulative_taxable, 2),
+        "cumulative_tax": round(cumulative_tax, 2),
+        "prior_tax_paid": round(prior_tax_paid, 2),
+        "brackets_used": bracket_hit,
+        "has_history": has_history,
+        "note": note,
+    }