feat: 角色视觉体系（头像按角色取）+ 时间注入（loop 每轮当前时间）

【角色视觉体系（红线：每个角色自己的头像/背景，绝不串用昔涟）】
- persona.go：Persona 加 Visual{avatar, chatBackground{landscape,portrait}} + DefaultAvatar；每个角色各自配。
- cyrene.yaml：昔涟配 avatar(3F-Q-Happy-1) + chatBackground(横/竖屏)。
- PersonaStore 加 Persona(id)；PersonaSummary 加 avatar/chatBackground；collectPersonas 按角色取
  Persona(id) 视觉（无视觉→空，前端回退默认占位，绝不串角色）。
- 前端：types PersonaRecord 加 avatar/chatBackground；persona.ts personaAvatar(p)=p?.avatar||默认占位
  (殊无昔涟 fallback)；store 加 currentPersona；App 挂载 fetchPersonas 取默认角色；
  TopBar/chat 头像改 personaAvatar(currentPersona)（写死昔涟头像已清除）。

【时间注入（她自然知道现在几点，深夜催睡交给人格/capacity）】
- options.go Options 加 Timezone；loop.go Loop 加 timeLocation/timeZoneName + New 解析 + loadTimezone；
  time.go currentTimeBlock()(当前时间+周几+时区，每轮刷新)；memory.go assembleContext 在「工作记忆」
  前注入时间 system(keyed 在 timeLocation!=nil，无时区不注入不破坏测试)；wire.go Timezone=a.cfg.Timezone。

go build/vet/test 全绿(gateway/loop/persona)；前端 tsc/vite build 75模块绿。红线无写死昔涟头像。

internal/runtime/loop/time.go

@@ -0,0 +1,42 @@
+package loop
+
+import (
+	"fmt"
+	"log/slog"
+	"time"
+
+	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/model"
+)
+
+// weekdaysCN maps time.Weekday (0=Sunday) to a Chinese weekday label.
+var weekdaysCN = [...]string{"周日", "周一", "周二", "周三", "周四", "周五", "周六"}
+
+// loadTimezone resolves the configured IANA timezone into a *time.Location for
+// the per-round time injection. An empty name (or one that fails to load) yields
+// nil, disabling injection entirely (backward compatible, graceful degradation).
+func loadTimezone(name string, log *slog.Logger) (*time.Location, string) {
+	if name == "" {
+		return nil, ""
+	}
+	loc, err := time.LoadLocation(name)
+	if err != nil {
+		log.Warn("timezone load failed; time injection disabled", "tz", name, "error", err)
+		return nil, ""
+	}
+	return loc, name
+}
+
+// currentTimeBlock renders one per-round "current time" system message so the
+// model knows the wall-clock time each round (not a first-turn snapshot). It is
+// called from assembleContext only when a timezone was configured. It provides
+// the raw clock — whether it is "late and time to sleep" is the persona prompt's
+// job, not a hard-coded rule here.
+func (l *Loop) currentTimeBlock() model.Message {
+	now := time.Now().In(l.timeLocation)
+	text := fmt.Sprintf("当前时间：%s %s，时区 %s",
+		now.Format("2006-01-02 15:04"),
+		weekdaysCN[now.Weekday()],
+		l.timeZoneName,
+	)
+	return model.TextMessage(model.RoleSystem, text)
+}