feat: stream real-time progress for agent SDK install/upgrade/uninstall

Replace the spinner-only UX with live log output during agent SDK
operations, matching the existing OpenCode plugin install experience.

Backend: emit structured events (started/log/completed/failed) via
EventEmitter during npm install and binary download. npm commands now
run with piped stdio for line-by-line streaming; binary downloads
report chunked progress every 1 MB.

Frontend: subscribe to `app://agent-install` events through a new
`useAgentInstallStream` hook and render a theme-aware log terminal
below the preflight checks panel.

Also fixes the install log container in both agent settings and the
OpenCode plugins modal: auto-scroll no longer shifts the outer page,
and colours now follow the active light/dark theme.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/lib/tauri.ts

@@ -172,9 +172,10 @@ export async function acpClearBinaryCache(agentType: AgentType): Promise<void> {
 }
 
 export async function acpDownloadAgentBinary(
-  agentType: AgentType
+  agentType: AgentType,
+  taskId: string
 ): Promise<void> {
-  return invoke("acp_download_agent_binary", { agentType })
+  return invoke("acp_download_agent_binary", { agentType, taskId })
 }
 
 export async function acpDetectAgentLocalVersion(
@@ -185,16 +186,21 @@ export async function acpDetectAgentLocalVersion(
 
 export async function acpPrepareNpxAgent(
   agentType: AgentType,
-  registryVersion?: string | null
+  registryVersion: string | null | undefined,
+  taskId: string
 ): Promise<string> {
   return invoke("acp_prepare_npx_agent", {
     agentType,
     registryVersion: registryVersion ?? null,
+    taskId,
   })
 }
 
-export async function acpUninstallAgent(agentType: AgentType): Promise<void> {
-  return invoke("acp_uninstall_agent", { agentType })
+export async function acpUninstallAgent(
+  agentType: AgentType,
+  taskId: string
+): Promise<void> {
+  return invoke("acp_uninstall_agent", { agentType, taskId })
 }
 
 export async function acpUpdateAgentPreferences(