Fix subagent announce failover race (always emit lifecycle end + treat timeout=0 as no-timeout) (#6621)

* Fix subagent announce race and timeout handling

Bug 1: Subagent announce fires before model failover retries finish
- Problem: CLI provider emitted lifecycle error on each attempt, causing
  subagent registry to prematurely call beginSubagentCleanup() and announce
  with incorrect status before failover retries completed
- Fix: Removed lifecycle error emission from CLI provider's attempt-level
  .catch() in agent-runner-execution.ts. Errors still propagate to
  runWithModelFallback for retry, but no intermediate lifecycle events
  are emitted. Only the final outcome (after all retries) emits lifecycle
  events.

Bug 2: Hard 600s per-prompt timeout ignores runTimeoutSeconds=0
- Problem: When runTimeoutSeconds=0 (meaning 'no timeout'), the code
  returned the default 600s timeout instead of respecting the 0 setting
- Fix: Modified resolveAgentTimeoutMs() to treat 0 as 'no timeout' and
  return a very large timeout value (30 days) instead of the default.
  This avoids setTimeout issues with Infinity while effectively providing
  unlimited time for long-running tasks.

* fix: emit lifecycle:error for CLI failures (#6621) (thanks @tyler6204)

* chore: satisfy format/lint gates (#6621) (thanks @tyler6204)

* fix: restore build after upstream type changes (#6621) (thanks @tyler6204)

* test: fix createSystemPromptOverride tests to match new return type (#6621) (thanks @tyler6204)

src/agents/pi-embedded-runner/system-prompt.ts

@@ -74,11 +74,8 @@ export function buildEmbeddedSystemPrompt(params: {
   });
 }
 
-export function createSystemPromptOverride(
-  systemPrompt: string,
-): (defaultPrompt?: string) => string {
-  const override = systemPrompt.trim();
-  return (_defaultPrompt?: string) => override;
+export function createSystemPromptOverride(systemPrompt: string): string {
+  return systemPrompt.trim();
 }
 
 export function applySystemPromptOverrideToSession(session: AgentSession, override: string) {