[FEATURE] Add planStorage setting to configure plans directory location

Feature Request

Add a planStorage setting to settings.json that allows users to configure where plan files are stored.

Current Behavior

Plan mode creates files in ~/.claude/plans/ (global home directory) with no option to change this location.

Requested Behavior

Add a planStorage setting in settings.json with options:

{
  "planStorage": "project"  // or "global" (default)
}

• "project": Store plans in .claude/plans/ within the current project directory
• "global": Store plans in ~/.claude/plans/ (current default behavior)

Use Cases

1. Project-specific context: Plans are often tightly coupled to the project being worked on. Storing them in the project directory keeps related artifacts together.

1. Version control: Teams may want to commit plans to track planning decisions alongside code.

1. Multi-project workflows: When working across multiple projects, having plans in each project directory prevents confusion about which plan belongs where.

1. Privacy/isolation: Some projects may have sensitive planning information that shouldn't be mixed with other project plans.

Alternative Considered

A more flexible approach could accept a path:

{
  "planStorage": ".claude/plans"  // relative to project root
}

Or support both project and global settings levels, where project-level settings.json can override the global default.

Related

• Issue #12366 mentions this concern: "Plans should be stored in project .claude dir IMHO"