agent: 更智能的 LLM provider 调度（byModel 精确路由 + AUTO 优先级链）

吸收 llmsproxy 的调度思想适配 HomeAgent“一源一模型”结构：
- RoutableProvider{Model,Priority} 次级接口（不破坏既有 Provider 实现）
- ProviderManager.OrderedProviders 改为按 (优先级 desc, 可用, 默认优先) 稳定排序，
  AUTO/空模型走该优先级链
- 新增 ProviderManager.ResolveForModel：精确模型名路由到归属源，找不到回落 AUTO 链
- LuaAdaptedProvider 不再无条件覆写 req.Model；显式模型名原样转发
- LLMSource.Priority + core.llm.sources.<name>.priority 配置项
- process.go: 显式模型走 ResolveForModel，AUTO 走 OrderedProviders
- 新增路由单测（优先级排序 + byModel 解析）

验证: go test ./... 27 包 0 失败；Windows 交叉编译通过；部署后服务健康

internal/agent/api/router_test.go

@@ -0,0 +1,66 @@
+package api
+
+import (
+	"context"
+	"testing"
+)
+
+// stubRoutableProvider implements both Provider and RoutableProvider.
+type stubRoutableProvider struct {
+	name    string
+	model   string
+	prio    int
+}
+
+func (s *stubRoutableProvider) Name() string          { return s.name }
+func (s *stubRoutableProvider) Model() string         { return s.model }
+func (s *stubRoutableProvider) Priority() int         { return s.prio }
+func (s *stubRoutableProvider) MaxContextTokens() int { return 4096 }
+func (s *stubRoutableProvider) Chat(context.Context, *CompletionRequest) (*CompletionResponse, error) {
+	return &CompletionResponse{Content: s.name}, nil
+}
+func (s *stubRoutableProvider) ChatStream(context.Context, *CompletionRequest) (<-chan StreamChunk, error) {
+	ch := make(chan StreamChunk, 1)
+	ch <- StreamChunk{Done: true}
+	return ch, nil
+}
+
+func TestProviderManagerPriorityOrder(t *testing.T) {
+	m := NewProviderManager()
+	m.Register("low", &stubRoutableProvider{name: "low", prio: 10})
+	m.Register("high", &stubRoutableProvider{name: "high", prio: 90})
+	m.Register("mid", &stubRoutableProvider{name: "mid", prio: 50})
+
+	got := m.OrderedProviders()
+	wantOrder := []string{"high", "mid", "low"}
+	for i, p := range got {
+		if p.Name() != wantOrder[i] {
+			t.Fatalf("order[%d] = %s, want %s (full=%v)", i, p.Name(), wantOrder[i], names(got))
+		}
+	}
+}
+
+func TestProviderManagerResolveForModel(t *testing.T) {
+	m := NewProviderManager()
+	m.Register("a", &stubRoutableProvider{name: "a", model: "gpt-5"})
+	m.Register("b", &stubRoutableProvider{name: "b", model: "deepseek"})
+
+	got := m.ResolveForModel("deepseek")
+	if len(got) == 0 || got[0].Name() != "b" {
+		t.Fatalf("resolve deepseek: got %v", names(got))
+	}
+
+	// 未知模型回落 AUTO 链（仍按优先级）
+	got2 := m.ResolveForModel("unknown")
+	if len(got2) == 0 {
+		t.Fatal("unknown model should fall back to auto chain")
+	}
+}
+
+func names(ps []Provider) []string {
+	out := make([]string, len(ps))
+	for i, p := range ps {
+		out[i] = p.Name()
+	}
+	return out
+}