feat(context-injector): introduce centralized context collection and integrate with keyword-detector

- Add ContextCollector class for managing and merging context entries across sessions
- Add types and interfaces for context management (ContextEntry, ContextPriority, PendingContext)
- Create context-injector hook for injection coordination
- Refactor keyword-detector to use context-injector instead of hook-message-injector
- Update src/index.ts to initialize context-injector infrastructure

🤖 Generated with assistance of OhMyOpenCode (https://github.com/code-yeongyu/oh-my-opencode)

src/features/context-injector/index.ts

@@ -0,0 +1,12 @@
+export { ContextCollector, contextCollector } from "./collector"
+export { injectPendingContext, createContextInjectorHook } from "./injector"
+export type {
+  ContextSourceType,
+  ContextPriority,
+  ContextEntry,
+  RegisterContextOptions,
+  PendingContext,
+  MessageContext,
+  OutputParts,
+  InjectionStrategy,
+} from "./types"