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/add-provider-config.ts

@@ -0,0 +1,54 @@
+import { writeFileSync } from "node:fs"
+import type { ConfigMergeResult, InstallConfig } from "../types"
+import { getConfigDir } from "./config-context"
+import { ensureConfigDirectoryExists } from "./ensure-config-directory-exists"
+import { formatErrorWithSuggestion } from "./format-error-with-suggestion"
+import { detectConfigFormat } from "./opencode-config-format"
+import { parseOpenCodeConfigFileWithError, type OpenCodeConfig } from "./parse-opencode-config-file"
+import { ANTIGRAVITY_PROVIDER_CONFIG } from "./antigravity-provider-configuration"
+
+export function addProviderConfig(config: InstallConfig): ConfigMergeResult {
+  try {
+    ensureConfigDirectoryExists()
+  } catch (err) {
+    return {
+      success: false,
+      configPath: getConfigDir(),
+      error: formatErrorWithSuggestion(err, "create config directory"),
+    }
+  }
+
+  const { format, path } = detectConfigFormat()
+
+  try {
+    let existingConfig: OpenCodeConfig | null = null
+    if (format !== "none") {
+      const parseResult = parseOpenCodeConfigFileWithError(path)
+      if (parseResult.error && !parseResult.config) {
+        existingConfig = {}
+      } else {
+        existingConfig = parseResult.config
+      }
+    }
+
+    const newConfig = { ...(existingConfig ?? {}) }
+    const providers = (newConfig.provider ?? {}) as Record<string, unknown>
+
+    if (config.hasGemini) {
+      providers.google = ANTIGRAVITY_PROVIDER_CONFIG.google
+    }
+
+    if (Object.keys(providers).length > 0) {
+      newConfig.provider = providers
+    }
+
+    writeFileSync(path, JSON.stringify(newConfig, null, 2) + "\n")
+    return { success: true, configPath: path }
+  } catch (err) {
+    return {
+      success: false,
+      configPath: path,
+      error: formatErrorWithSuggestion(err, "add provider config"),
+    }
+  }
+}