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/shared/tmux/tmux-utils/server-health.ts

@@ -0,0 +1,47 @@
+let serverAvailable: boolean | null = null
+let serverCheckUrl: string | null = null
+
+function delay(milliseconds: number): Promise<void> {
+	return new Promise((resolve) => setTimeout(resolve, milliseconds))
+}
+
+export async function isServerRunning(serverUrl: string): Promise<boolean> {
+	if (serverCheckUrl === serverUrl && serverAvailable === true) {
+		return true
+	}
+
+	const healthUrl = new URL("/health", serverUrl).toString()
+	const timeoutMs = 3000
+	const maxAttempts = 2
+
+	for (let attempt = 1; attempt <= maxAttempts; attempt++) {
+		const controller = new AbortController()
+		const timeout = setTimeout(() => controller.abort(), timeoutMs)
+
+		try {
+			const response = await fetch(healthUrl, {
+				signal: controller.signal,
+			}).catch(() => null)
+			clearTimeout(timeout)
+
+			if (response?.ok) {
+				serverCheckUrl = serverUrl
+				serverAvailable = true
+				return true
+			}
+		} finally {
+			clearTimeout(timeout)
+		}
+
+		if (attempt < maxAttempts) {
+			await delay(250)
+		}
+	}
+
+	return false
+}
+
+export function resetServerCheck(): void {
+	serverAvailable = null
+	serverCheckUrl = null
+}