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/shared/agent-variant.ts

@@ -1,8 +1,8 @@
-import type { OhMyOpenCodeConfig } from "../config"
+import type { OhMyOpenAgentConfig } from "../config"
 import { AGENT_MODEL_REQUIREMENTS, CATEGORY_MODEL_REQUIREMENTS } from "./model-requirements"
 
 export function resolveAgentVariant(
-  config: OhMyOpenCodeConfig,
+  config: OhMyOpenAgentConfig,
   agentName?: string
 ): string | undefined {
   if (!agentName) {
@@ -33,7 +33,7 @@ export function resolveAgentVariant(
 }
 
 export function resolveVariantForModel(
-  config: OhMyOpenCodeConfig,
+  config: OhMyOpenAgentConfig,
   agentName: string,
   currentModel: { providerID: string; modelID: string },
 ): string | undefined {
@@ -87,7 +87,7 @@ function findVariantInChain(
 }
 
 export function applyAgentVariant(
-  config: OhMyOpenCodeConfig,
+  config: OhMyOpenAgentConfig,
   agentName: string | undefined,
   message: { variant?: string }
 ): void {