feat: 垂懸字避免（方案 C，斷行層無測量，order 70）（§6.5.1）

段末行 CJK 實義字數 ≥ N（預設 2；標點／符號不計）。standalone 段落級 pass：
自段末向前數 N 個實義字，把「第 N 字起至段末」（含其間／尾隨標點）包入
<jz-orphan>（white-space:nowrap）。該整體不可斷 → 末行恒含之 ⇒ 末行實義字 ≥ N，
任意寬度／字型／瀏覽器成立，無需量測 layout。

要點：
- 邊界字定位跨 jz-jinze／行內元素攀爬：實義字落於行內元素內時綁定整個塊級
  直接子（不切割 nowrap 群、revert 乾淨）；僅裸文本直接子才精確切分（最小綁定）。
- 僅處理葉段落（無塊級後代）；段落實義字 < N 不綁；單行段方案 C 本就無害。
- 選項 orphan?: boolean | { chars? }；**預設開 chars=2**（§6.5.6 建議）；
  下游可 orphan:false 關閉。段落級，data-jz-level=text 子樹自動跳過。
- order=70：jinze(40)／spacing(50)／longWord(60) 後、layout pass(90/92) 前。

新增 _orphan.css（jz-orphan{white-space:nowrap}）；JzTag 加 jz-orphan。
9 項單元測試（末 N＋尾標點、chars 選項、標點不計、實義字<N 不綁、跨 jinze、
關閉、冪等、revert、段落級閘）。共 85 測試全綠。

窄容器拖動「末行恒 ≥N」之 layout 驗證留待 demo（Step 4-5，瀏覽器）。

src/index.ts

@@ -13,9 +13,10 @@ import { jiyaAdjacencyPass, jiyaPass } from "./typeset/jiya.js";
 import { jinzePass } from "./typeset/jinze.js";
 import { gapTrimPass, lineEdgePass } from "./typeset/lineedge.js";
 import { longWordPass } from "./typeset/longword.js";
+import { orphanPass } from "./typeset/orphan.js";
 import { spacingPass } from "./typeset/spacing.js";
 import { resolveRuleset } from "./core/unicode.js";
-import type { BiasTable, JiyaOptions, JuzhenOptions, LongWordOptions, Pass, RenderContext, ResolvedOptions } from "./types.js";
+import type { BiasTable, JiyaOptions, JuzhenOptions, LongWordOptions, OrphanOptions, Pass, RenderContext, ResolvedOptions } from "./types.js";
 
 export type { JuzhenOptions, ResolvedOptions, Pass };
 export type { CharClassOverride, BdSubclass, Ruleset, Bias, BiasTable } from "./types.js";
@@ -41,7 +42,7 @@ const DEFAULT_SKIP_TAGS = [
 
 const PASSES: Pass[] = [
     jiyaPass, jiyaAdjacencyPass, longWordPass, spacingPass, jinzePass,
-    lineEdgePass, gapTrimPass,
+    orphanPass, lineEdgePass, gapTrimPass,
 ];
 
 function feature(v: unknown, dflt: boolean): boolean
@@ -58,6 +59,16 @@ function resolveLongWord(v: boolean | LongWordOptions | undefined): { minLength:
     return { minLength, lang };
 }
 
+function resolveOrphan(v: boolean | OrphanOptions | undefined): { chars: number }
+{
+    if (v && typeof v === "object")
+    {
+        const chars = typeof v.chars === "number" && v.chars >= 1 ? Math.floor(v.chars) : 2;
+        return { chars };
+    }
+    return { chars: 2 };
+}
+
 function resolveJiya(
     v: boolean | JiyaOptions | undefined,
 ): { halfWidth: "halt" | "margin"; bias: BiasTable }
@@ -97,12 +108,14 @@ export function normalizeOptions(opts: JuzhenOptions = {}): ResolvedOptions
             longWord: opts.longWord === false ? false : feature(opts.longWord, true),
             jiya: feature(opts.jiya, true),
             jinze: feature(opts.jinze, true),
+            orphan: opts.orphan === false ? false : feature(opts.orphan, true),
             hanging: feature(opts.hanging, false),
             biaodian: feature(opts.biaodian, false),
             emphasis: feature(opts.emphasis, false),
             ruby: feature(opts.ruby, false),
         },
         longWord: resolveLongWord(opts.longWord),
+        orphan: resolveOrphan(opts.orphan),
         jiyaConfig: resolveJiya(opts.jiya),
         blocks: Array.isArray(opts.blocks) ? opts.blocks.slice() : [],
         finder: {