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/config/schema/tmux.ts

@@ -0,0 +1,20 @@
+import { z } from "zod"
+
+export const TmuxLayoutSchema = z.enum([
+  "main-horizontal", // main pane top, agent panes bottom stack
+  "main-vertical", // main pane left, agent panes right stack (default)
+  "tiled", // all panes same size grid
+  "even-horizontal", // all panes horizontal row
+  "even-vertical", // all panes vertical stack
+])
+
+export const TmuxConfigSchema = z.object({
+  enabled: z.boolean().default(false),
+  layout: TmuxLayoutSchema.default("main-vertical"),
+  main_pane_size: z.number().min(20).max(80).default(60),
+  main_pane_min_width: z.number().min(40).default(120),
+  agent_pane_min_width: z.number().min(20).default(40),
+})
+
+export type TmuxConfig = z.infer<typeof TmuxConfigSchema>
+export type TmuxLayout = z.infer<typeof TmuxLayoutSchema>