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.

script/build-schema-document.ts

@@ -1,8 +1,8 @@
 import * as z from "zod"
-import { OhMyOpenCodeConfigSchema } from "../src/config/schema"
+import { OhMyOpenAgentConfigSchema } from "../src/config/schema"
 
 export function createOhMyOpenCodeJsonSchema(): Record<string, unknown> {
-  const jsonSchema = z.toJSONSchema(OhMyOpenCodeConfigSchema, {
+  const jsonSchema = z.toJSONSchema(OhMyOpenAgentConfigSchema, {
     target: "draft-7",
     unrepresentable: "any",
   })