feat: kbagent job verify — post-execution validation

[padak]

Problem

job run --wait returns status: success, but the agent has no way to verify the actual outcome:

• Were the expected rows loaded?
• Did the schema change unexpectedly?
• Is the row count within normal range?

The agent has to manually chain storage table-detail + row count checks + schema comparison.

Proposal

kbagent job verify --project prod --job-id 456

Output:

• Row counts (loaded vs expected based on recent history)
• Schema diff (if columns changed)
• Data freshness check
• Anomaly flags (e.g., "0 rows loaded but last 7 runs averaged 1,200")

Use case

Critical for agents that run pipelines autonomously — they need confidence that "success" means "actually worked correctly," not just "didn't crash."

Context

Discussion from Devil's Advocate analysis of kbagent's agentic capabilities.

[padak]

Part of #152 (Modern Agentic CLI epic).