修正 JSON 位元組相容與 xref Unicode 邊界（審核意見）

依 #12 審核意見修正四項偏差，並補一項同源問題：

1. iterXrefs 前一字元檢查改 Unicode：isWordChar 改用
   unicode.IsLetter/IsDigit，且以 utf8 正確解碼前一 rune
   （原版只認 ASCII 又取單一位元組）。另補齊 Python finditer
   的重試語義：起點被 lookbehind 擋下時從下一 rune 重試，
   否則「修復bear-cli#9」會整段丟失（Python 匹配後半 cli#9）；
   lookbehind 字元集含 #（##5 不匹配）。
2. writeJSON 改 json.Encoder + SetEscapeHTML(false)：
   Python ensure_ascii=False 不轉義 <、>、&，json.Marshal 預設
   會，標題含這些字元即失去位元組相容。
3. stalled_hours 改 strconv.FormatFloat(v,'f',1,64)：整數值輸出
   48.0（原 %g 輸出 48，極大值還會變 1e+06）。
4. Child.last_activity_at 無可解析時刻時輸出 null（原輸出 ""），
   型別改 *string；格式對齊 FormatMoment（UTC 記 +00:00 非 Z）。
5. cmd/xcheck 輸出同樣停用 HTML 轉義（Marshal* 對自訂
   MarshalJSON 的輸出仍會轉義）。

驗證：go build/vet/test 全綠（16 測試函式，新增 CJK、##5、
全形數字、HTML 字元、48.0、null 等案例）；cmd/xcheck 與
gitea.py stalled 對真實 API 並行掃描輸出位元組相同（1749B，
含 bear-cli#9 父追蹤項與 5 子項摘要）；--xrefs 對 CJK
邊界輸入與 Python 一致。

internal/workflow/workflow_test.go

@@ -5,9 +5,11 @@
 package workflow
 
 import (
+	"bytes"
 	"encoding/json"
 	"errors"
 	"fmt"
+	"strings"
 	"testing"
 	"time"
 )
@@ -86,6 +88,12 @@ func TestIterXrefsEdges(t *testing.T) {
 		{"斜線後不切半段", "alterminal/bear#47 只應匹配整段", [][2]string{{"alterminal/bear", "47"}}},
 		{"連字號 repo 名", "bear-cli#9", [][2]string{{"bear-cli", "9"}}},
 		{"路徑後的 #N 不匹配", "see https://x/a/#frag not #5", [][2]string{{"", "5"}}},
+		// Python \w 是 Unicode：CJK 緊鄰 #N 時整體視為 \w，lookbehind 擋下。
+		{"CJK 緊鄰 #N 略過", "修復#12的問題，見 #5", [][2]string{{"", "5"}}},
+		{"CJK 緊鄰 repo#N 整段略過", "修復agents#12", nil},
+		{"CJK 緊鄰連字號 repo 匹配後半", "修復bear-cli#9 見 #5", [][2]string{{"cli", "9"}, {"", "5"}}},
+		{"連續井號", "##5", nil},
+		{"全形數字後 #N", "１２#5", nil},
 	}
 	for _, tc := range cases {
 		t.Run(tc.name, func(t *testing.T) {
@@ -424,30 +432,48 @@ func TestScanStalledSkipsPRsInIssues(t *testing.T) {
 	}
 }
 
-// TestItemJSON 輸出欄位與 gitea.py 對齊（last_activity_at 序列化、omitempty）。
+// TestItemJSON 與 gitea.py 的 JSON 位元組相容（鍵序、HTML 不轉義、48.0、null）。
 func TestItemJSON(t *testing.T) {
 	ts := at(-600)
+	activity := FormatMoment(ts)
 	item := Item{
-		Type: "issue", Repo: "alterminal/teai", Number: 7, Title: "t", URL: "u",
+		Type: "issue", Repo: "alterminal/teai", Number: 7, Title: "R,D <v2> & 規劃", URL: "u",
 		Assignees: []string{"ceo"}, LastCommentBy: "max",
-		LastActivityAt: ts, StalledHours: 10, Reason: "assignee-idle",
-		ChildActivity: []Child{{Repo: "alterminal/teai", Number: 3, Title: "父", State: "open", LastActivityAt: ts.Format(time.RFC3339)}},
+		LastActivityAt: ts, StalledHours: 48, Reason: "assignee-idle",
+		ChildActivity: []Child{
+			{Repo: "alterminal/teai", Number: 3, Title: "父", State: "open", LastActivityAt: &activity},
+			{Repo: "alterminal/teai", Number: 4, Title: "無時刻", State: "open"},
+		},
+	}
+	// json.Marshal 會把 <、>、& 重新轉義，必須用停用 HTML 轉義的編碼器。
+	var buf bytes.Buffer
+	enc := json.NewEncoder(&buf)
+	enc.SetEscapeHTML(false)
+	if err := enc.Encode(item); err != nil {
+		t.Fatalf("Encode: %v", err)
+	}
+	got := strings.TrimSuffix(buf.String(), "\n")
+	want := `{"type":"issue","repo":"alterminal/teai","number":7,"title":"R,D <v2> & 規劃","url":"u","assignees":["ceo"],"last_comment_by":"max","last_activity_at":"2026-09-09T22:00:00+00:00","stalled_hours":48.0,"reason":"assignee-idle","child_activity":[{"repo":"alterminal/teai","number":3,"title":"父","state":"open","last_activity_at":"2026-09-09T22:00:00+00:00"},{"repo":"alterminal/teai","number":4,"title":"無時刻","state":"open","last_activity_at":null}]}`
+	if got != want {
+		t.Fatalf("JSON 位元組不相容:\n got %s\nwant %s", got, want)
+	}
+}
+
+// TestPullJSON：pull 的鍵序（author、reviewers）與非整數 stalled_hours。
+func TestPullJSON(t *testing.T) {
+	item := Item{
+		Type: "pull", Repo: "alterminal/teai", Number: 12, Title: "t", URL: "u",
+		Author: "ceo", Reviewers: []string{"queena"},
+		LastActivityAt: at(-600), StalledHours: 10.44, Reason: "reviewer-idle",
 	}
 	b, err := json.Marshal(item)
 	if err != nil {
 		t.Fatalf("Marshal: %v", err)
 	}
-	var m map[string]any
-	if err := json.Unmarshal(b, &m); err != nil {
-		t.Fatalf("Unmarshal: %v", err)
-	}
-	for _, key := range []string{"type", "repo", "number", "title", "url", "assignees", "last_comment_by", "last_activity_at", "stalled_hours", "reason", "child_activity"} {
-		if _, ok := m[key]; !ok {
-			t.Errorf("輸出缺少欄位 %q：%s", key, b)
-		}
-	}
-	if _, ok := m["author"]; ok {
-		t.Errorf("issue 不應輸出 author：%s", b)
+	got := string(b)
+	want := `{"type":"pull","repo":"alterminal/teai","number":12,"title":"t","url":"u","author":"ceo","reviewers":["queena"],"last_comment_by":"","last_activity_at":"2026-09-09T22:00:00+00:00","stalled_hours":10.4,"reason":"reviewer-idle"}`
+	if got != want {
+		t.Fatalf("JSON 位元組不相容:\n got %s\nwant %s", got, want)
 	}
 }