bug: Exclude ARCHIVED pseudo-agent from agent selection dropdowns

[moltar-bot]

Summary

ARCHIVED appears in agent-selection dropdowns, but it is not a runnable agent and should not be selectable for agent-targeted operations.

Impact

• Misleading UX: users can select a non-agent target.
• Risk of invalid cron/job configurations and confusing failures.

Reproduction

1. Open Scheduler → Create Job (or other agent-select UI).
2. Open the Agent dropdown.
3. Observe that Archived / archived appears as an option.

Actual

• Archived pseudo-agent is included in generic agent lists used for selection.

Expected

• Archived workspace remains available for browsing where relevant.
• Archived entry is excluded from runnable/targetable agent selectors (scheduler, execution targets, etc.).

Notes / Suspected Areas

• Archived pseudo-agent is appended in shared agent store:
  • web/src/stores/agentStore.js
• Some views already filter it (TaskManagerOverview), but Scheduler create modal currently does not:
  • web/src/pages/CronJobs.jsx (Agent select uses agents.map(...) directly)

Acceptance Criteria

• Archived is filtered out of all agent-targeting selectors.
• Archived remains visible only in contexts where archived workspace browsing is intended.
• Add regression tests for selector filtering behavior.