feat!: 账号池改渠道网关,对外协议换成 vivid /v1

- 新增 channels/channel_models:上游 URL + AES-GCM 加密 key +
  并发/权重/本地统计,模型经渠道 /v1/models 导入绑定
- internal/upstream:vivid 协议客户端(NDJSON 流 + jobId 断流重连 +
  uploads 预签名 + models + balance + 错误分类)
- service/v1 重写:权重分组调度、Redis 并发槽 conc:c:、故障转移,
  站内/测试/对外统一走渠道执行器
- 对外端点换成 vivid 四件套:POST /v1/generate(NDJSON+jobId 重连)、
  POST /v1/uploads(SigV4 预签名 PUT)、GET /v1/models、GET /v1/balance,
  错误包 {"error":{"code","message"}}
- API key 新发改 vk_+48hex;删除全部内置 provider 与 token 池
- 管理端:渠道 CRUD/拉模型/导入/余额端点,前端账号页换渠道页,
  概览/文档/测试弹窗适配

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

backend/internal/util/mediadur.go

@@ -0,0 +1,138 @@
+package util
+
+import (
+	"bytes"
+	"encoding/binary"
+	"math"
+)
+
+// maxMediaDurationSec 时长 sanity 上限：解析出超过 24h 视为垃圾数据丢弃。
+const maxMediaDurationSec = 24 * 3600
+
+// MediaDurationSeconds 从已读片段尽力解析媒体时长（秒）。
+// mp4/mov/m4a 扫描 mvhd 盒子；webm 解 EBML Duration×TimecodeScale；wav 按
+// byteRate 换算。解析不出返回 false——调用方可用文件尾片段再试一次
+// （未 faststart 的 mp4 moov 盒子常在文件尾）。mp3/ogg 无廉价可靠头长度，跳过。
+func MediaDurationSeconds(mime string, buf []byte) (float64, bool) {
+	if len(buf) == 0 {
+		return 0, false
+	}
+	var sec float64
+	var ok bool
+	switch mime {
+	case "video/mp4", "video/quicktime", "audio/mp4":
+		sec, ok = mvhdDuration(buf)
+	case "video/webm":
+		sec, ok = webmDuration(buf)
+	case "audio/wav":
+		sec, ok = wavDuration(buf)
+	}
+	if !ok || sec <= 0 || sec > maxMediaDurationSec {
+		return 0, false
+	}
+	return sec, true
+}
+
+// mvhdDuration 在缓冲里扫 "mvhd" 盒子并解析 duration/timescale。
+// 盒子布局：[size4][type4=mvhd][version1][flags3]
+// v0: creation4 mod4 timescale4 duration4 → timescale@idx+16, duration@idx+20
+// v1: creation8 mod8 timescale4 duration8 → timescale@idx+24, duration@idx+28
+func mvhdDuration(buf []byte) (float64, bool) {
+	for off := 0; ; {
+		i := bytes.Index(buf[off:], []byte("mvhd"))
+		if i < 0 {
+			return 0, false
+		}
+		i += off
+		if ver := buf[i+4]; ver == 0 && i+24 <= len(buf) {
+			ts := binary.BigEndian.Uint32(buf[i+16 : i+20])
+			dur := binary.BigEndian.Uint32(buf[i+20 : i+24])
+			if ts > 0 && dur > 0 {
+				return float64(dur) / float64(ts), true
+			}
+		} else if ver == 1 && i+36 <= len(buf) {
+			ts := binary.BigEndian.Uint32(buf[i+24 : i+28])
+			dur := binary.BigEndian.Uint64(buf[i+28 : i+36])
+			if ts > 0 && dur > 0 {
+				return float64(dur) / float64(ts), true
+			}
+		}
+		off = i + 4
+	}
+}
+
+// webmDuration 扫 EBML Duration 元素（0x4489，float）和 TimecodeScale
+// （0x2AD7B1，uint，缺省 1,000,000ns）。秒 = duration × scale / 1e9。
+func webmDuration(buf []byte) (float64, bool) {
+	scale := uint64(1_000_000)
+	if i := bytes.Index(buf, []byte{0x2a, 0xd7, 0xb1}); i >= 0 {
+		if v, n := ebmlVint(buf[i+3:]); n > 0 && i+3+n+v <= len(buf) {
+			scale = 0
+			for _, b := range buf[i+3+n : i+3+n+v] {
+				scale = scale<<8 | uint64(b)
+			}
+			if scale == 0 {
+				scale = 1_000_000
+			}
+		}
+	}
+	i := bytes.Index(buf, []byte{0x44, 0x89})
+	if i < 0 {
+		return 0, false
+	}
+	v, n := ebmlVint(buf[i+2:])
+	if n == 0 || i+2+n+v > len(buf) {
+		return 0, false
+	}
+	f := buf[i+2+n : i+2+n+v]
+	var dur float64
+	switch v {
+	case 4:
+		dur = float64(math.Float32frombits(binary.BigEndian.Uint32(f)))
+	case 8:
+		dur = math.Float64frombits(binary.BigEndian.Uint64(f))
+	default:
+		return 0, false
+	}
+	return dur * float64(scale) / 1e9, true
+}
+
+// ebmlVint 读 EBML 变长整数的长度值：返回 (负载长度, vint 本身字节数)。
+func ebmlVint(buf []byte) (int, int) {
+	if len(buf) == 0 {
+		return 0, 0
+	}
+	for n := 1; n <= 8; n++ {
+		mask := byte(0x80 >> (n - 1))
+		if buf[0]&mask != 0 {
+			if len(buf) < n {
+				return 0, 0
+			}
+			v := int(buf[0] &^ mask)
+			for i := 1; i < n; i++ {
+				v = v<<8 | int(buf[i])
+			}
+			return v, n
+		}
+	}
+	return 0, 0
+}
+
+// wavDuration 解析 RIFF/WAVE：byteRate@28(LE u32) + "data" 块大小换算秒数。
+func wavDuration(buf []byte) (float64, bool) {
+	if len(buf) < 44 || string(buf[:4]) != "RIFF" || string(buf[8:12]) != "WAVE" {
+		return 0, false
+	}
+	rate := binary.LittleEndian.Uint32(buf[28:32])
+	if rate == 0 {
+		return 0, false
+	}
+	for off := 12; off+8 <= len(buf); {
+		size := int(binary.LittleEndian.Uint32(buf[off+4 : off+8]))
+		if string(buf[off:off+4]) == "data" {
+			return float64(size) / float64(rate), true
+		}
+		off += 8 + size + size&1 // 块按 2 字节对齐
+	}
+	return 0, false
+}