chore: recommend compact cadence for long taskMaestro sessions

[JeremyDev87]

Purpose

Long sessions (6+ hours) accumulate massive context, degrading response quality and increasing cost.

Solution

Add recommendation to parallel-orchestrator and taskMaestro docs:

• Compact after every 2 waves
• Compact before starting a new batch of waves
• Save critical state to context.md before compact

References

• This session ran 6+ hours without compact
• Parent: Improve taskMaestro orchestration reliability (session 2 retrospective) #900

[JeremyDev87]

Implemented in PR #918 (batch update)