refactor: remove terminal agent concept entirely

Remove the "agent can be a terminal" branching from the entire codebase.
An agent is now always a session-backed chat agent. Standalone terminal
infrastructure (terminal component, ANSI handling, terminal-stream-protocol)
is preserved.

Server: delete ManagedTerminalAgent, AgentKind, TerminalExitDetails,
launchTerminalAgent, registerTerminalAgent, handleTerminalAgentExited,
supportsTerminalMode capability, buildTerminalCreate/ResumeCommand from
all providers, terminal agent persistence/projections.

App: delete terminal-agent-panel.tsx, terminal-agent-reopen-store.ts,
terminal/terminalExit fields on agent state, "Terminal Agents" launcher
section, terminal-agent workspace setup flow, terminal badge in agent list.

CLI: remove terminal column from ls, terminal-agent error from send.

60 files changed, -3592 lines

packages/app/e2e/helpers/workspace-lifecycle.ts

@@ -1,11 +1,9 @@
 import { expect, type Page } from "@playwright/test";
 import {
   clickNewChat,
-  clickProviderTile,
   clickTerminal,
   countTabsOfKind,
   getTabTestIds,
-  waitForTabWithTitle,
 } from "./launcher";
 import { setupDeterministicPrompt, waitForTerminalContent } from "./terminal-perf";
 
@@ -35,13 +33,6 @@ export async function createStandaloneTerminalFromLauncher(page: Page): Promise<
   await expect.poll(async () => (await getTabTestIds(page)).length).toBe(tabIdsBefore.length);
 }
 
-export async function createTerminalAgentFromLauncher(page: Page, providerLabel: string): Promise<void> {
-  await clickProviderTile(page, providerLabel);
-  await expect(page.getByTestId("terminal-agent-loading")).toHaveCount(0, { timeout: 30_000 });
-  await expect(terminalSurface(page)).toBeVisible({ timeout: 30_000 });
-  await waitForTabWithTitle(page, /new agent/i);
-}
-
 export async function createAgentChatFromLauncher(page: Page): Promise<void> {
   await clickNewChat(page);
   await expect(composerInput(page)).toBeVisible({ timeout: 15_000 });