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/auto-update-checker/checker/package-json-locator.ts

@@ -0,0 +1,30 @@
+import * as fs from "node:fs"
+import * as path from "node:path"
+import type { PackageJson } from "../types"
+import { PACKAGE_NAME } from "../constants"
+
+export function findPackageJsonUp(startPath: string): string | null {
+  try {
+    const stat = fs.statSync(startPath)
+    let dir = stat.isDirectory() ? startPath : path.dirname(startPath)
+
+    for (let i = 0; i < 10; i++) {
+      const pkgPath = path.join(dir, "package.json")
+      if (fs.existsSync(pkgPath)) {
+        try {
+          const content = fs.readFileSync(pkgPath, "utf-8")
+          const pkg = JSON.parse(content) as PackageJson
+          if (pkg.name === PACKAGE_NAME) return pkgPath
+        } catch {
+          // ignore
+        }
+      }
+      const parent = path.dirname(dir)
+      if (parent === dir) break
+      dir = parent
+    }
+  } catch {
+    // ignore
+  }
+  return null
+}