FE-864: raise pi action timeout to 600s

Each cook agent action (write-tests, write-code, verify-epic) runs under a
per-action wall-clock budget enforced in pi-actions.ts. Raise the default
from 300s to 600s so Sonnet agents have headroom on larger slices and on
brownfield repos where setup/discovery eats into the turn.

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

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

Author: kostandinang

src/orchestrator/src/pi-actions.ts

@@ -59,7 +59,7 @@ function logVerbose(output: string): void {
 // Pi dispatch
 // ---------------------------------------------------------------------------
 
-const PI_TIMEOUT_MS = 300_000;
+const PI_TIMEOUT_MS = 600_000;
 // Output cap — the timeout alone won't stop a fast, chatty agent.
 const PI_MAX_OUTPUT = 10 * 1024 * 1024;