Pipeline scheduler - task-to-agent orchestration

Omni/Pipeline becomes the orchestrator that connects tasks, fund, and agentd:

1. Periodically scans task ready per namespace/domain 2. Checks fund for available budget in that domain 3. If budget available → spawns agent via agentd, tagged with domain 4. Agent works tasks, cost accumulates against domain budget 5. Agent finishes → sets task to review status 6. Loop

This replaces ad-hoc agent spawning with a systematic scheduler. Each domain's agent only works tasks in its namespace, only if it has budget.

Dependencies: fund command (for budget checks), agentd domain tagging, task inbox/review workflow (t-608).

The pipeline should be independently runnable (cron, systemd timer, or long-lived process) and Ava can also trigger it manually.