chore(agents): strengthen Knowledge Gap, restructure snip section, add openspec-review command

[tedivm]

Summary

Hardens AGENTS.md guidance and adds a new /openspec-review command.

What Changed

• Knowledge Gap — Stronger language: training data is stale/unreliable, no exceptions or shortcuts for verification
• snip section — Code blocks converted to inline commands for cleaner formatting
• snip section — Added Docker-specific guidance with BAD/GOOD examples
• snip section — Added token savings/costs explanation after the table
• commands/openspec-review.md — New /openspec-review command for reviewing design, tasks, and specs

Reviewer Focus

• Knowledge Gap language strength — is it appropriately forceful?
• snip section restructuring — anything lost from the original ("When to skip", "Check token savings")?
• openspec-review command scope — is the prompt sufficient?