[Feature Request] Implement project-scoped plan storage to prevent cross-project plan interference

Bug Description
internal plans dir filled with plans from separate projects, when asking claude to review "the original plan" after a few compacts it tries, lists all plans in the dir, says there are too many plans and instead of looking at the most recent ones does a search across all plans for keywords, i feel this is causing false positives, how about having plans scoped to separate projects? or auto archiving after some time or a cap?

Environment Info

• Platform: darwin
• Terminal: ghostty
• Version: 2.0.72
• Feedback ID: 98364293-87ed-4ef3-931c-a5066714787b