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/hook/startup-toasts.ts

@@ -0,0 +1,22 @@
+import type { PluginInput } from "@opencode-ai/plugin"
+import { log } from "../../../shared/logger"
+import { showSpinnerToast } from "./spinner-toast"
+
+export async function showVersionToast(ctx: PluginInput, version: string | null, message: string): Promise<void> {
+  const displayVersion = version ?? "unknown"
+  await showSpinnerToast(ctx, displayVersion, message)
+  log(`[auto-update-checker] Startup toast shown: v${displayVersion}`)
+}
+
+export async function showLocalDevToast(
+  ctx: PluginInput,
+  version: string | null,
+  isSisyphusEnabled: boolean
+): Promise<void> {
+  const displayVersion = version ?? "dev"
+  const message = isSisyphusEnabled
+    ? "Sisyphus running in local development mode."
+    : "Running in local development mode. oMoMoMo..."
+  await showSpinnerToast(ctx, `${displayVersion} (dev)`, message)
+  log(`[auto-update-checker] Local dev toast shown: v${displayVersion}`)
+}