[FEATURE] per-project data directory (store sessions/memory inside project folder)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Claude Code stores all project data (session transcripts, memory files) under ~/.claude/projects/<project-hash>/. This path is fixed and non-configurable per project.

This makes it impossible to keep all project-related Claude data self-contained inside the project directory. Moving or sharing a project means losing its entire conversation history and memory.

Proposed Solution

add a per-project setting (e.g. in .claude/settings.json) that redirects where Claude Code stores data for that specific project:

{
  "dataDir": ".claude/history"
}

### Alternative Solutions

_No response_

### Priority

Medium - Would be very helpful

### Feature Category

CLI commands and flags

### Use Case Example

_No response_

### Additional Context

_No response_