feat(plugins): 服务路径/适配器名冲突进裁决而非崩溃或硬拒绝（用户要求 A+B）

此前两类冲突各有问题：
A) 两个插件声明同一条 /api/plugins/http/ 服务路径 → 分发器按加载顺序静默
   选一个（装个新插件就可能改变既有路径归属）。
B) 插件装与内置/他插件同名的适配器 → 硬错误 ErrAdapterNameReserved / owned by。

用户要求：都改成「报冲突、列出候选、运维选一个保留、选择持久化」，绝不崩溃
或拒绝启动。

## A 类：插件 HTTP 服务路径冲突
- dispatch（plugin_http_routes.go）同路径多认领时不再 load-order 选边：未裁决
  返回 409 并点名候选；已裁决按赢家分发。
- route_conflicts.go：RouteConflicts/RouteWinner/ResolveRouteConflict，只统计
  loaded 且未禁用的插件；赢家插件若不再声明该路径，裁决作废回未裁决态。

## B 类：适配器名冲突
- InstallAdapter 撞名（内置或他插件所有）不再硬拒，改挂起：现任继续服务，候选
  入 AdapterConflicts，返回 typed ErrAdapterConflictPending（区分「代码错」）。
- ResolveAdapterConflict：incumbent 保留现任 / candidate 真正装上插件版（绕过
  reserved 门禁——这是运维显式授权覆盖内置的唯一入口）并转移归属。
- 现任内置永不被静默覆盖，守住「第三方插件不得篡改内核发行物」信任边界。

## 持久化 + WebAPI + WebUI
- 两张裁决表落 .route-conflicts.json（routes + adapters），LoadDir 时读回；
  重启后插件再装同名适配器自动套用上次裁决。
- WebAPI：GET /api/plugins/conflicts 列冲突；POST {kind,path|name,winner} 裁决。
- WebUI：插件页顶部「冲突裁决」卡片，逐条列路径/适配器冲突 + 候选 + 裁决按钮。

## 测试
- 单测 conflict_arbitration_test.go 6 项全过：路径冲突检测/裁决/持久化/重启、
  赢家消失回退、适配器撞名挂起/incumbent/candidate/归属转移、非法 winner 拒绝、
  自身更新不受影响（token 轮换不走冲突路径）。
- e2e conflict_arbitration_e2e_test.go 2 项全过（真二进制）：两插件抢路径→409
  点名→裁决→200 赢家应答→/v1/models 无回归；插件装 shadow openai→挂起→现任
  保留→裁决 candidate→插件版生效→冲突清空。
- 全量 build + vet 通过，既有 lua/gateway/core 回归无破坏。

修正过程中发现并修了一个真 bug：LoadAdapterSource 对 key≠declared 的适配器
重装会建第二个池、留旧池继续服务（v2 装了 v1 还在跑）——改成统一按注册键
归档，裁决 candidate 后新版本才真正生效。

internal/lua/vm.go

@@ -841,12 +841,35 @@ func (v *VM) LoadAdapterSource(name, code string) error {
 	// it controls while shipping an adapter that declares the name sources
 	// reference). Without this, updating that adapter would install a second
 	// pool and leave the old one serving traffic.
+	//
+	// The key can live under EITHER name (this is the "reload replaces the same
+	// pool entry rather than silently registering a second one" rule):
+	//
+	//   - pools[static.name]  — the pool filed under the DECLARED name (the
+	//     common case, and the only case when a plugin installs under a key that
+	//     matches its script's own name), or
+	// The pool registry is keyed by the DECLARED name (static.name), always:
+	// first install files pools[static.name], and a reload replaces that same
+	// slot. registeredAs only RECORDS the registration key for reverse lookups
+	// (EffectiveAdapterName scans for it); it is not a second key space.
+	//
+	// An earlier version redirected the key to prev.static.registeredAs here,
+	// assuming pools were filed under the registration key — but first installs
+	// file under the declared name, so that redirect created a SECOND pool and
+	// left the old one serving whenever key≠declared (a real bug: a v2 install
+	// via arbitration left v1 serving, and UpdateAdapter had the same hole).
 	key := static.name
-	if prev, ok := v.pools[key]; ok && prev.static.registeredAs != "" {
-		key = prev.static.registeredAs
-	}
 	old := v.pools[key]
-	p := newAdapterPool(static.name, code, *static)
+	// The new pool MUST be filed under the SAME slot as the old one (key), and
+	// named after that slot, so a later lookup by either the DECLARED name or
+	// the REGISTRATION KEY finds the one live pool. Naming it after static.name
+	// would move the pool to the declared-name slot when the incumbent lived
+	// under the registration key, leaving the registration-key slot pointing at
+	// the stale (old) pool that shutdown() then tears down — callers reading by
+	// the registration key see "adapter missing", callers by declared name see
+	// a pool that isn't the one serving. key is the stable identity; the
+	// declared name is reachable through static.name.
+	p := newAdapterPool(key, code, *static)
 	p.setMax(maxW)
 	// Carry the revision forward so the new source keeps counting ABOVE the old
 	// one. A cache keyed on (vm, revision, name) must see a value different