Feature/project registry cli

[hanley-development]

Summary

Adds an optional local project registry and CLI commands for managing multiple ProjectMem projects from one installation.

The registry lets users register project directories, assign aliases and tags, select an active project, and resolve projects consistently across commands. Existing project-local workflows remain supported.

What changed

• Added versioned project registry persistence at:
  • $PROJECTMEM_HOME/projects.json
  • ~/.projectmem/projects.json by default
• Added project registration, removal, listing, inspection, detection, and active-project selection.
• Added project aliases, brain assignments, and tags.
• Added pjm project CLI commands for managing the registry.
• Added support for preregistering an existing directory with --allow-uninitialized.
• Added canonical path and strict registry-data validation.
• Added actionable CLI errors for missing or invalid projects.
• Documented registry usage in README.md and TUTORIAL.md.
• Documented the registry’s local data and security boundaries in SECURITY.md.

Compatibility

• Existing projects do not need to use the global registry.
• Normal registration requires an initialized .projectmem/ directory.
• --allow-uninitialized may be used to preregister another existing directory.
• Registry data remains local-only.
• No telemetry or network transfer was added.
• Existing public function signatures and CLI entry points remain unchanged.

Validation

• Focused registry and CLI tests: 43 passed
• Full test suite: 177 passed, 1 skipped
• Ruff: passed
• Git whitespace check: passed
• Independent code review: no remaining Critical or Important findings

Scope

This PR contains only the project registry and project management CLI feature, its tests, review fixes, and related documentation.

Base branch: main
Feature branch: feature/project-registry-cli
Dependencies on other feature branches: none