Plans should be stored in project folder, not global ~/.claude/plans/

Problem

Currently all plans are stored in a single global folder ~/.claude/plans/ regardless of which project they belong to.

When working with multiple projects, this creates confusion:

• Plans from different projects are mixed together
• No way to know which plan belongs to which project without reading content
• When switching between projects, old plans from other projects are still visible

Current behavior

~/.claude/plans/
├── plan-for-project-A.md
├── plan-for-project-B.md  
└── plan-for-project-C.md   # All mixed together

Expected behavior

Plans should be stored in the project's .claude/plans/ folder:

/path/to/project-A/.claude/plans/
└── some-plan.md

/path/to/project-B/.claude/plans/
└── another-plan.md

Benefits

1. Clear separation between projects
2. Plans are version-controlled with the project (if desired)
3. Easy to clean up plans for specific project
4. No confusion about which plan belongs where
5. Consistent with how other project-specific files are stored in .claude/

Workaround

Currently I have to manually check plan content to determine which project it belongs to.