feat(compat): package rename compatibility layer for oh-my-opencode → oh-my-openagent

- Add legacy plugin startup warning when oh-my-opencode config detected
- Update CLI installer and TUI installer for new package name
- Split monolithic config-manager.test.ts into focused test modules
- Add plugin config detection tests for legacy name fallback
- Update processed-command-store to use plugin-identity constants
- Add claude-code-plugin-loader discovery test for both config names
- Update chat-params and ultrawork-db tests for plugin identity

Part of #2823

src/cli/tui-installer.ts

@@ -1,5 +1,6 @@
 import * as p from "@clack/prompts"
 import color from "picocolors"
+import { PLUGIN_NAME } from "../shared"
 import type { InstallArgs } from "./types"
 import {
   addPluginToOpenCodeConfig,
@@ -43,7 +44,7 @@ export async function runTuiInstaller(args: InstallArgs, version: string): Promi
   const config = await promptInstallConfig(detected)
   if (!config) return 1
 
-  spinner.start("Adding oh-my-opencode to OpenCode config")
+  spinner.start(`Adding ${PLUGIN_NAME} to OpenCode config`)
   const pluginResult = await addPluginToOpenCodeConfig(version)
   if (!pluginResult.success) {
     spinner.stop(`Failed to add plugin: ${pluginResult.error}`)
@@ -52,7 +53,7 @@ export async function runTuiInstaller(args: InstallArgs, version: string): Promi
   }
   spinner.stop(`Plugin added to ${color.cyan(pluginResult.configPath)}`)
 
-  spinner.start("Writing oh-my-opencode configuration")
+  spinner.start(`Writing ${PLUGIN_NAME} configuration`)
   const omoResult = writeOmoConfig(config)
   if (!omoResult.success) {
     spinner.stop(`Failed to write config: ${omoResult.error}`)