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/shared/plugin-config-detection.test.ts

@@ -0,0 +1,23 @@
+import { describe, expect, test } from "bun:test"
+import { existsSync, mkdirSync, rmSync, writeFileSync } from "node:fs"
+import { join } from "node:path"
+import { detectPluginConfigFile } from "./jsonc-parser"
+
+describe("detectPluginConfigFile - canonical config detection", () => {
+  const testDir = join(__dirname, ".test-detect-plugin-canonical")
+
+  test("detects oh-my-openagent config when no legacy config exists", () => {
+    //#given
+    if (!existsSync(testDir)) mkdirSync(testDir, { recursive: true })
+    writeFileSync(join(testDir, "oh-my-openagent.jsonc"), "{}")
+
+    //#when
+    const result = detectPluginConfigFile(testDir)
+
+    //#then
+    expect(result.format).toBe("jsonc")
+    expect(result.path).toBe(join(testDir, "oh-my-openagent.jsonc"))
+
+    rmSync(testDir, { recursive: true, force: true })
+  })
+})