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/layout.ts

@@ -0,0 +1,49 @@
+import { spawn } from "bun"
+import type { TmuxLayout } from "../../../config/schema"
+import { getTmuxPath } from "../../../tools/interactive-bash/tmux-path-resolver"
+
+export async function applyLayout(
+	tmux: string,
+	layout: TmuxLayout,
+	mainPaneSize: number,
+): Promise<void> {
+	const layoutProc = spawn([tmux, "select-layout", layout], {
+		stdout: "ignore",
+		stderr: "ignore",
+	})
+	await layoutProc.exited
+
+	if (layout.startsWith("main-")) {
+		const dimension =
+			layout === "main-horizontal" ? "main-pane-height" : "main-pane-width"
+		const sizeProc = spawn(
+			[tmux, "set-window-option", dimension, `${mainPaneSize}%`],
+			{ stdout: "ignore", stderr: "ignore" },
+		)
+		await sizeProc.exited
+	}
+}
+
+export async function enforceMainPaneWidth(
+	mainPaneId: string,
+	windowWidth: number,
+): Promise<void> {
+	const { log } = await import("../../logger")
+	const tmux = await getTmuxPath()
+	if (!tmux) return
+
+	const dividerWidth = 1
+	const mainWidth = Math.floor((windowWidth - dividerWidth) / 2)
+
+	const proc = spawn([tmux, "resize-pane", "-t", mainPaneId, "-x", String(mainWidth)], {
+		stdout: "ignore",
+		stderr: "ignore",
+	})
+	await proc.exited
+
+	log("[enforceMainPaneWidth] main pane resized", {
+		mainPaneId,
+		mainWidth,
+		windowWidth,
+	})
+}