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/cli/doctor/checks/model-resolution-config.ts

@@ -1,9 +1,10 @@
+import { PLUGIN_NAME } from "../../../shared/plugin-identity"
 import { readFileSync } from "node:fs"
 import { join } from "node:path"
 import { detectConfigFile, getOpenCodeConfigPaths, parseJsonc } from "../../../shared"
 import type { OmoConfig } from "./model-resolution-types"
 
-const PACKAGE_NAME = "oh-my-opencode"
+const PACKAGE_NAME = PLUGIN_NAME
 const USER_CONFIG_BASE = join(
   getOpenCodeConfigPaths({ binary: "opencode", version: null }).configDir,
   PACKAGE_NAME