refactor: remove orphaned compaction-context-injector hook

Hook was disconnected from plugin flow since commit 4a82ff40.
Never called at runtime, superseded by preemptive-compaction hook.

src/hooks/index.ts

@@ -9,7 +9,6 @@ export { createDirectoryReadmeInjectorHook } from "./directory-readme-injector";
 export { createEmptyTaskResponseDetectorHook } from "./empty-task-response-detector";
 export { createAnthropicContextWindowLimitRecoveryHook, type AnthropicContextWindowLimitRecoveryOptions } from "./anthropic-context-window-limit-recovery";
 
-export { createCompactionContextInjector } from "./compaction-context-injector";
 export { createThinkModeHook } from "./think-mode";
 export { createClaudeCodeHooksHook } from "./claude-code-hooks";
 export { createRulesInjectorHook } from "./rules-injector";