refactor: remove dcp_for_compaction and preemptive_compaction features

- Delete src/hooks/preemptive-compaction/ entirely
- Remove dcp_for_compaction from schema and executor
- Clean up related imports, options, and test code
- Update READMEs to remove experimental options docs

src/hooks/compaction-context-injector/index.ts

@@ -1,7 +1,14 @@
-import type { SummarizeContext } from "../preemptive-compaction"
 import { injectHookMessage } from "../../features/hook-message-injector"
 import { log } from "../../shared/logger"
 
+export interface SummarizeContext {
+  sessionID: string
+  providerID: string
+  modelID: string
+  usageRatio: number
+  directory: string
+}
+
 const SUMMARIZE_CONTEXT_PROMPT = `[COMPACTION CONTEXT INJECTION]
 
 When summarizing this session, you MUST include the following sections in your summary: