refactor: 拆分 cockpit 為可個別安裝的 statusbar 與 companion

- statusbar：輸入框上方狀態列，指令 /statusbar
- companion：小說角色陪伴，指令 /companion，自行渲染角色行
- companion 資料目錄改為 ~/.companion
- 整併 M4 檔案至 companion；M2 實作移至 hooks/companion/persona
- README 移除本機資料夾安裝，補上更新與移除指令

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

plugins/companion/hooks/register.tsx

@@ -0,0 +1,49 @@
+import type { Register } from 'claude-code'
+
+import { fitCompanion } from './companion/band'
+import { createCompanion } from './companion/core'
+import { nodeFs } from './companion/node-fs'
+
+let companion: ReturnType<typeof createCompanion> | undefined
+
+export const register: Register = on => {
+  on('session.start', async ($, e, next) => {
+    await $.command.register({
+      name: 'companion',
+      description: '角色陪伴控制：狀態、切換角色、關閉、使用者設定',
+      argumentHint: 'status | switch <角色> | off | setup',
+    })
+    const home = await $.env.get('HOME')
+    companion = createCompanion({ fs: nodeFs, clock: { now: Date.now }, root: `${home ?? ''}/.companion` })
+    const first = await companion.ensureActivated()
+    if (first.first) $.ui.toast(`已啟用 ${first.name}。用 /companion off 可關閉`)
+
+    return next(e)
+  })
+
+  on('command.run', { command: 'companion' }, async ($, e) => ({
+    text: companion ? await companion.command(e.args) : '尚未就緒。',
+  }))
+
+  on('ui.render', { component: 'AbovePrompt' }, async ($, e, next) => {
+    const rest = await next(e)
+    const view = await companion?.view()
+    if (e.props.hasSurvey || !view) return rest
+
+    const line = fitCompanion(view, e.props.bodyColumns)
+    const { Box, Text } = $.ui.resolve(e)
+
+    return (
+      <Box flexDirection="column">
+        {rest}
+        <Text wrap="truncate">
+          {line.map(s => (
+            <Text color={s.color} dimColor={s.dim} bold={s.bold}>
+              {s.text}
+            </Text>
+          ))}
+        </Text>
+      </Box>
+    )
+  })
+}