Add list_folders for project move destination discovery

[deverman]

Summary

• add list_folders MCP tool and focusrelay list-folders CLI command for project move destination discovery
• add shared FolderItem output model, bridge request/response plumbing, pagination, and compact field selection
• update move_projects docs/tool descriptions to point users to list_folders instead of requiring known folder IDs

Validation

• node --check Plugin/FocusRelayBridge.omnijs/Resources/BridgeLibrary.js
• git diff --check origin/master..HEAD
• swift test
• ./scripts/install-plugin.sh, full OmniFocus restart, bridge-health-check
• live smoke: ./.build/debug/focusrelay list-folders --fields id,name --limit 5
• live smoke: ./.build/debug/focusrelay list-folders --fields id,name,parentID,parentName,projectCount,childFolderCount --limit 2

Closes #53

[deverman]

Merge order note: this PR is stacked on #52 (issue-36-ai-optimized-mutation-docs) and should not be merged until the mutation-docs PR and its lower-stack dependencies are merged. This PR closes #53 and only adds folder read/discovery support for move_projects; it does not change mutation semantics.