Spike: PTY-based Claude Code integration with multi-agent concurrency

Proves that spawning `claude -p` in a pseudo-terminal from Rust gets Max
subscription billing (apiKeySource: "none", rateLimitType: "five_hour")
instead of per-token API charges. Concurrent agents run in parallel PTY
sessions with session resumption via --resume for multi-turn conversations.

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

frontend/src/components/ChatHeader.tsx

@@ -175,6 +175,11 @@ export function ChatHeader({
 							backgroundSize: "10px",
 						}}
 					>
+						<optgroup label="Claude Code (PTY)">
+							<option value="claude-code-pty">
+								claude-code-pty
+							</option>
+						</optgroup>
 						{(claudeModels.length > 0 || !hasAnthropicKey) && (
 							<optgroup label="Anthropic">
 								{claudeModels.length > 0 ? (