refactor: rename OhMyOpenCode types to OhMyOpenAgent and centralize PACKAGE_NAME

- Rename all PascalCase types: OhMyOpenCodePlugin → OhMyOpenAgentPlugin, etc.
- 231 OhMyOpenAgent references across ~60 files
- Centralize 4 PACKAGE_NAME constants to import from plugin-identity.ts
- Update src/plugin-config.ts to use CONFIG_BASENAME from plugin-identity

Wave 3 Tasks 5 & 6 complete.

src/plugin-handlers/config-handler-formatter.test.ts

@@ -1,6 +1,6 @@
 import { afterEach, beforeEach, describe, expect, spyOn, test } from "bun:test"
 
-import type { OhMyOpenCodeConfig } from "../config"
+import type { OhMyOpenAgentConfig } from "../config"
 import { createConfigHandler } from "./config-handler"
 import * as agentConfigHandler from "./agent-config-handler"
 import * as commandConfigHandler from "./command-config-handler"
@@ -62,7 +62,7 @@ afterEach(() => {
 describe("createConfigHandler formatter pass-through", () => {
   test("preserves formatter object configured in opencode config", async () => {
     // given
-    const pluginConfig: OhMyOpenCodeConfig = {}
+    const pluginConfig: OhMyOpenAgentConfig = {}
     const formatterConfig = {
       prettier: {
         command: ["prettier", "--write"],
@@ -98,7 +98,7 @@ describe("createConfigHandler formatter pass-through", () => {
 
   test("preserves formatter=false configured in opencode config", async () => {
     // given
-    const pluginConfig: OhMyOpenCodeConfig = {}
+    const pluginConfig: OhMyOpenAgentConfig = {}
     const config: Record<string, unknown> = {
       formatter: false,
     }