feat(agents): support per-agent displayName for i18n (#4004)

Add optional `displayName` field to AgentOverrideConfigSchema (next to
the existing `color` field) so users can specify localized agent names
in oh-my-openagent.json:

  { "agents": { "sisyphus": { "displayName": "总指挥" } } }

When set, the override takes precedence everywhere
AGENT_DISPLAY_NAMES[agentName] is used — TUI agent selector, the
agent list key, and the internal `name` field. When not set, behavior
is identical to before (hardcoded English names from AGENT_DISPLAY_NAMES).

Implementation touches:
- AgentOverrideConfigSchema: adds displayName?: z.string().optional()
- getAgentDisplayName / getAgentListDisplayName: accept optional overrides
  map and check displayName before the hardcoded table
- remapAgentKeysToDisplayNames: forwards overrides map to name resolution
- agent-config-handler: passes pluginConfig.agents as the overrides map

Backward compatible — existing configs without displayName continue to
work unchanged.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/plugin-handlers/agent-key-remapper.ts

@@ -1,8 +1,11 @@
 import { getAgentListDisplayName } from "../shared/agent-display-names"
 
+type AgentOverridesMap = Record<string, { displayName?: string } | undefined>
+
 function rewriteAgentNameForListDisplay(
   key: string,
   value: unknown,
+  overrides?: AgentOverridesMap,
 ): unknown {
   if (typeof value !== "object" || value === null) {
     return value
@@ -11,19 +14,20 @@ function rewriteAgentNameForListDisplay(
   const agent = value as Record<string, unknown>
   return {
     ...agent,
-    name: getAgentListDisplayName(key),
+    name: getAgentListDisplayName(key, overrides),
   }
 }
 
 export function remapAgentKeysToDisplayNames(
   agents: Record<string, unknown>,
+  overrides?: AgentOverridesMap,
 ): Record<string, unknown> {
   const result: Record<string, unknown> = {}
 
   for (const [key, value] of Object.entries(agents)) {
-    const displayName = getAgentListDisplayName(key)
+    const displayName = getAgentListDisplayName(key, overrides)
     if (displayName && displayName !== key) {
-      result[displayName] = rewriteAgentNameForListDisplay(key, value)
+      result[displayName] = rewriteAgentNameForListDisplay(key, value, overrides)
       // Regression guard: do not also assign result[key].
       // This line was repeatedly re-added and caused duplicate agent rows in the UI.
       // Runtime callers that previously depended on config-key aliases were fixed in: