refactor(session-recovery): extract storage utilities to separate module

Split session-recovery.ts into modular structure:
- types.ts: SDK-aligned type definitions
- constants.ts: storage paths and part type sets
- storage.ts: reusable read/write operations
- index.ts: main recovery hook logic

src/hooks/session-recovery/constants.ts

@@ -0,0 +1,10 @@
+import { join } from "node:path"
+import { xdgData } from "xdg-basedir"
+
+export const OPENCODE_STORAGE = join(xdgData ?? "", "opencode", "storage")
+export const MESSAGE_STORAGE = join(OPENCODE_STORAGE, "message")
+export const PART_STORAGE = join(OPENCODE_STORAGE, "part")
+
+export const THINKING_TYPES = new Set(["thinking", "redacted_thinking", "reasoning"])
+export const META_TYPES = new Set(["step-start", "step-finish"])
+export const CONTENT_TYPES = new Set(["text", "tool", "tool_use", "tool_result"])