fix: prevent stale subagent data from showing in windows

- Reduce getRecentSubagents window from 60 to 15 minutes
- Skip old/completed agents when restoring window states (10 min cutoff)
- Clear old activity data when new agent with same ID is discovered
- Force close existing window for agentId before opening fresh one

Fixes issue where old prompts/input from previous Ralph Loop runs
were displayed when clicking on subagent windows.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/web/server.ts

@@ -4600,7 +4600,7 @@ NOW: Generate the implementation plan for the task above. Think step by step.`;
       scheduledRuns: Array.from(this.scheduledRuns.values()),
       respawnStatus,
       globalStats: this.store.getAggregateStats(activeSessionTokens),
-      subagents: subagentWatcher.getRecentSubagents(60), // Last hour of subagent activity
+      subagents: subagentWatcher.getRecentSubagents(15), // Last 15 min - filter out stale agents from previous runs
       timestamp: Date.now(),
     };
   }
@@ -4630,7 +4630,7 @@ NOW: Generate the implementation plan for the task above. Think step by step.`;
       scheduledRuns: Array.from(this.scheduledRuns.values()),
       respawnStatus,
       globalStats: this.store.getAggregateStats(activeSessionTokens),
-      subagents: subagentWatcher.getRecentSubagents(60),
+      subagents: subagentWatcher.getRecentSubagents(15), // 15 min to avoid stale agents
       timestamp: Date.now(),
     };
   }