refactor(sdk)!: 废除自定协议号，版本身份只由版本号本身承载

兼容性判据原有三处自造版本号，全部删除：
  - procProtocolVersion（模板侧握手常量）
  - shmVersion / shmOffVersion（共享段 header）
  - unifiedVersion（SuperBlock）

为什么废除：语义版本变动频繁（修 bug、加字段），再要求人去升一个额外的号，
那个号必然漏升而腐烂。实证：ProtocolVersion 常量在多次布局变更里只升过一次，
而对应的守卫测试（TestProcTemplate_ShmLayoutMatchesKernel）长期处于失败状态
无人察觉 —— 它当时期望 shmStageFieldCount=18/shmVersion=1，实际已是 19/2。

取而代之的两个判据都是**结构的派生事实**，不需要谁记得去同步：
  1. 主版本号：内核 meta.Version ↔ 插件 sdk.SDKVersion 的主版本段比对。
     主版本跃迁正是破坏性变更的定义（1.0.0 从 C ABI 改子进程即属此列），
     所以它天然是正确分界。
  2. field_count：StageContext 描述符个数，决定标志位基址。

顺带修正了 shmFlagsOff：原实现用本插件的编译期常量推算标志位基址，
内核加字段时会静默错位。现改为从 header 读取内核下发的描述符个数。
SuperBlock 的 version 槽位保留（不动其余偏移），值不再写入也不再校验。

判据：TestProcTemplate_RejectsIncompatiblePeer（含 banned 列表，
防这些号被重新引入）。

README_EN.md

@@ -52,7 +52,7 @@ has been withdrawn — any SDK tag with a non-zero patch position is wrong.)
 **Upgrading a 1.0.x plugin to 1.1.x: no code changes, no rebuild.** Everything added in 1.1.0 is
 in the "plugin calls, kernel implements" direction, so not calling it means not being affected
 (verified with an old `plugin.bin` built against SDK 0.9.2: it handshakes fine on the new kernel,
-because the handshake validates `ProtocolVersion`, not the SDK version). Rebuild only when you want
+because the handshake validates the **major** version, not the exact SDK version). Rebuild only when you want
 the new fields.
 
 **Upgrading a 1.1.x plugin to 1.2.x: the interface is purely additive, but a rebuild is required.**
@@ -526,8 +526,8 @@ Internal plugins (platform built-in) have full SDK access including SocialAPI wr
 
 **Prebuilt example artifacts ship with every release**: besides the 5-platform `hmapdev`, an SDK
 release contains the example plugins' `.hmap` files plus `SHA256SUMS`/`MANIFEST.txt`. The reason is
-that plugin binaries are **protocol-bound** to the kernel (`ProtocolVersion` + the shared-memory
-magic), so shipping the toolchain without matching artifacts invites installing an old artifact —
+that plugin binaries are **layout-bound** to the kernel (major version + unified-region magic +
+`field_count`), so shipping the toolchain without matching artifacts invites installing an old artifact —
 which fails the handshake and looks like "the plugin is broken" rather than "the versions don't
 match".