feat: W7 功能標籤分類、對白檢索與注入 (#8)

用 $.model.complete（Haiku）判斷回應的功能標籤，從角色索引取同標籤對白，
以只增不改的訊息附在使用者訊息之前；失敗一律退回不注入。

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

plugins/anime-companion/hooks/inject.ts

@@ -0,0 +1,31 @@
+import { CHARACTERS, type CharacterCode } from './characters'
+import { classify, type Complete } from './classify'
+import type { Config } from './config'
+import { formatExamples } from './examples'
+import { retrieve, type IndexEntry } from './retrieval'
+
+export type InjectDeps = {
+  config: Config
+  indexes: Readonly<Record<CharacterCode, readonly IndexEntry[]>>
+  complete: Complete
+  append: (text: string) => Promise<unknown>
+  now: () => number
+  turn: number
+}
+
+// 回傳 null 表示這一輪不注入（沒選角色、強度 0、索引為空、分類失敗或沒有同標籤的對白）。
+// 索引為空時不呼叫模型，省下一次無用的分類。
+export async function buildInjection(
+  { config, indexes, complete, now, turn }: Omit<InjectDeps, 'append'>,
+  userText: string,
+): Promise<{ text: string | null; fn: string | null; ms: number } | null> {
+  const character = config.character
+  if (character === null || config.intensity === 0) return null
+  const index = indexes[character]
+  if (index.length === 0) return null
+  const started = now()
+  const fn = await classify(complete, userText)
+  const ms = now() - started
+  if (fn === null) return { text: null, fn: null, ms }
+  return { text: formatExamples(CHARACTERS[character].name, retrieve(index, fn, { turn })), fn, ms }
+}