Daemon: --agent flag on cron commands + multi-agent cron loading

[ludusrusso]

Parent PRD

#34

What to build

Two changes:

1. CLI: Add --agent flag to wildgecu cron add, cron ls, and cron rm. When provided, operates on the named agent's crons/ directory.
2. Daemon: At startup, scan all agents under agents/ and load their cron jobs into the scheduler. Each agent's cron jobs run with the agent's own model (resolved from config.yaml + global providers).

End-to-end: wildgecu cron add --agent=researcher creates a cron under agents/researcher/crons/. On daemon restart, the job runs with the researcher's model.

Acceptance criteria

• --agent flag on cron add, cron ls, cron rm
• Cron commands operate on agent's crons dir when flag is provided
• Daemon scans agents/ at startup and discovers all agents' cron directories
• Each agent's cron jobs are scheduled with the agent's own provider/model
• Cron results written to the agent's cron-results/ directory
• All jobs (main + all agents) run in one gocron.Scheduler
• When --agent is omitted, existing behavior preserved
• Daemon reload includes agent crons

Blocked by

• Blocked by Home.Agent: directory scaffolding for static subagents #41 (Home.Agent directory scaffolding)
• Blocked by Agent config.yaml: parsing and model resolution #42 (agent config.yaml parsing)

User stories addressed

• User story 9 (add cron to specific agent)
• User story 10 (list crons for specific agent)
• User story 14 (one daemon for all)
• User story 15 (daemon loads all agent crons)
• User story 16 (crons run with agent identity)