Feature Request: Global memory / cross-project shared memory

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

Memory is scoped per project (working directory). Switching directories means losing all memory — user profile, preferences, ongoing project context, everything.

Real example: I chat in Desktop\new-folder\, build up years of memories (personal profile, exam prep progress, RP progress, feedback preferences). Then I switch to C:\Users\me\ — completely blank slate.

User identity, personality, and preferences are cross-directory by nature. They shouldn't be severed by project boundaries.

Proposed Solution

Support ~/.claude/memory/ as a global memory layer that ALL projects load automatically, in addition to their local project memories. Or at minimum, allow specifying extra memory paths in settings.json:

{
  "memory": {
    "additionalPaths": ["~/.claude/global-memory"]
  }
}

### Alternative Solutions

_No response_

### Priority

Critical - Blocking my work

### Feature Category

CLI commands and flags

### Use Case Example

_No response_

### Additional Context

_No response_