feat(preemptive-compaction): add onBeforeSummarize callback and context injection

- Added BeforeSummarizeCallback type to allow injecting context before session summarization
- Added onBeforeSummarize option to PreemptiveCompactionOptions
- Created compaction-context-injector module that injects summarization instructions with sections:
  - User Requests (As-Is)
  - Final Goal
  - Work Completed
  - Remaining Tasks
  - MUST NOT Do (Critical Constraints)
- Wired up callback invocation in preemptive-compaction before calling summarize API
- Exported new hook from src/hooks/index.ts

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src/hooks/index.ts

@@ -8,7 +8,8 @@ export { createDirectoryAgentsInjectorHook } from "./directory-agents-injector";
 export { createDirectoryReadmeInjectorHook } from "./directory-readme-injector";
 export { createEmptyTaskResponseDetectorHook } from "./empty-task-response-detector";
 export { createAnthropicAutoCompactHook, type AnthropicAutoCompactOptions } from "./anthropic-auto-compact";
-export { createPreemptiveCompactionHook, type PreemptiveCompactionOptions } from "./preemptive-compaction";
+export { createPreemptiveCompactionHook, type PreemptiveCompactionOptions, type SummarizeContext, type BeforeSummarizeCallback } from "./preemptive-compaction";
+export { createCompactionContextInjector } from "./compaction-context-injector";
 export { createThinkModeHook } from "./think-mode";
 export { createClaudeCodeHooksHook } from "./claude-code-hooks";
 export { createRulesInjectorHook } from "./rules-injector";