refactor: use case-insensitive matching for agent names

Apply case-insensitive utilities across agents, delegation, and tool
restrictions. Removes duplicate implementations from agents/utils.ts.
Agent validation now normalizes input to canonical names.

src/shared/agent-tool-restrictions.ts

@@ -4,6 +4,8 @@
  * true = tool allowed, false = tool denied.
  */
 
+import { findCaseInsensitive } from "./case-insensitive"
+
 const EXPLORATION_AGENT_DENYLIST: Record<string, boolean> = {
   write: false,
   edit: false,
@@ -35,10 +37,10 @@ const AGENT_RESTRICTIONS: Record<string, Record<string, boolean>> = {
 }
 
 export function getAgentToolRestrictions(agentName: string): Record<string, boolean> {
-  return AGENT_RESTRICTIONS[agentName] ?? {}
+  return findCaseInsensitive(AGENT_RESTRICTIONS, agentName) ?? {}
 }
 
 export function hasAgentToolRestrictions(agentName: string): boolean {
-  const restrictions = AGENT_RESTRICTIONS[agentName]
+  const restrictions = findCaseInsensitive(AGENT_RESTRICTIONS, agentName)
   return restrictions !== undefined && Object.keys(restrictions).length > 0
 }