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/cli/config-manager/opencode-binary.ts

@@ -0,0 +1,40 @@
+import type { OpenCodeBinaryType } from "../../shared/opencode-config-dir-types"
+import { initConfigContext } from "./config-context"
+
+const OPENCODE_BINARIES = ["opencode", "opencode-desktop"] as const
+
+interface OpenCodeBinaryResult {
+  binary: OpenCodeBinaryType
+  version: string
+}
+
+async function findOpenCodeBinaryWithVersion(): Promise<OpenCodeBinaryResult | null> {
+  for (const binary of OPENCODE_BINARIES) {
+    try {
+      const proc = Bun.spawn([binary, "--version"], {
+        stdout: "pipe",
+        stderr: "pipe",
+      })
+      const output = await new Response(proc.stdout).text()
+      await proc.exited
+      if (proc.exitCode === 0) {
+        const version = output.trim()
+        initConfigContext(binary, version)
+        return { binary, version }
+      }
+    } catch {
+      continue
+    }
+  }
+  return null
+}
+
+export async function isOpenCodeInstalled(): Promise<boolean> {
+  const result = await findOpenCodeBinaryWithVersion()
+  return result !== null
+}
+
+export async function getOpenCodeVersion(): Promise<string | null> {
+  const result = await findOpenCodeBinaryWithVersion()
+  return result?.version ?? null
+}