refactor: wave 2 - split atlas, auto-update-checker, session-recovery, todo-enforcer, background-task hooks

- Extract atlas/ into 15 focused modules (hook, event handler, tool policies, types, etc.)
- Split auto-update-checker into checker/ and hook/ subdirectories with single-purpose files
- Decompose session-recovery into separate recovery strategy files per error type
- Extract todo-continuation-enforcer from monolith to directory with dedicated modules
- Split background-task/tools.ts into individual tool creator files
- Extract command-executor, tmux-utils into focused sub-modules
- Split config/schema.ts into domain-specific schema files
- Decompose cli/config-manager.ts into focused modules
- Rollback skill-mcp-manager, model-availability, index.ts splits that broke tests
- Fix all import path depths for moved files (../../ -> ../../../)
- Add explicit type annotations to resolve TS7006 implicit any errors

Typecheck: 0 errors
Tests: 2359 pass, 5 fail (all pre-existing)

src/hooks/session-recovery/storage/text-part-injector.ts

@@ -0,0 +1,30 @@
+import { existsSync, mkdirSync, writeFileSync } from "node:fs"
+import { join } from "node:path"
+import { PART_STORAGE } from "../constants"
+import type { StoredTextPart } from "../types"
+import { generatePartId } from "./part-id"
+
+export function injectTextPart(sessionID: string, messageID: string, text: string): boolean {
+  const partDir = join(PART_STORAGE, messageID)
+
+  if (!existsSync(partDir)) {
+    mkdirSync(partDir, { recursive: true })
+  }
+
+  const partId = generatePartId()
+  const part: StoredTextPart = {
+    id: partId,
+    sessionID,
+    messageID,
+    type: "text",
+    text,
+    synthetic: true,
+  }
+
+  try {
+    writeFileSync(join(partDir, `${partId}.json`), JSON.stringify(part, null, 2))
+    return true
+  } catch {
+    return false
+  }
+}