refactor(agent): consolidate agent system into unified AgentManager with provider-based architecture

Replace separate ACP and agent-types modules with unified AgentManager using provider pattern. Migrate Claude and Codex implementations to provider-specific clients. Streamline session-agent integration, remove old ACP notification types, and introduce agent timeline events. Delete obsolete documentation and test files. Add AgentRegistry for persistence and agent-stream-based communication pattern.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

packages/app/src/utils/agent-status.ts

@@ -0,0 +1,27 @@
+import type { Agent } from "@/contexts/session-context";
+
+type AgentStatus = Agent["status"];
+
+const STATUS_COLOR_MAP: Record<AgentStatus, string> = {
+  initializing: "#f59e0b",
+  idle: "#22c55e",
+  running: "#3b82f6",
+  error: "#ef4444",
+  closed: "#6b7280",
+};
+
+const STATUS_LABEL_MAP: Record<AgentStatus, string> = {
+  initializing: "Initializing",
+  idle: "Idle",
+  running: "Running",
+  error: "Error",
+  closed: "Closed",
+};
+
+export function getAgentStatusColor(status: AgentStatus): string {
+  return STATUS_COLOR_MAP[status] ?? "#9ca3af";
+}
+
+export function getAgentStatusLabel(status: AgentStatus): string {
+  return STATUS_LABEL_MAP[status] ?? "Unknown";
+}