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/pane-dimensions.ts

@@ -0,0 +1,28 @@
+import { spawn } from "bun"
+import { getTmuxPath } from "../../../tools/interactive-bash/tmux-path-resolver"
+
+export interface PaneDimensions {
+	paneWidth: number
+	windowWidth: number
+}
+
+export async function getPaneDimensions(
+	paneId: string,
+): Promise<PaneDimensions | null> {
+	const tmux = await getTmuxPath()
+	if (!tmux) return null
+
+	const proc = spawn(
+		[tmux, "display", "-p", "-t", paneId, "#{pane_width},#{window_width}"],
+		{ stdout: "pipe", stderr: "pipe" },
+	)
+	const exitCode = await proc.exited
+	const stdout = await new Response(proc.stdout).text()
+
+	if (exitCode !== 0) return null
+
+	const [paneWidth, windowWidth] = stdout.trim().split(",").map(Number)
+	if (Number.isNaN(paneWidth) || Number.isNaN(windowWidth)) return null
+
+	return { paneWidth, windowWidth }
+}