Add directory creation to the folder picker

[Ingress007]

Summary

• add a left-aligned New directory action to the directory picker footer
• open a compact, picker-styled dialog with Create and select, Create, and Cancel actions
• start directory browsing from the currently selected project, preserving the existing picker behavior
• create only one direct child of the browsed directory and report invalid names, conflicts, missing parents, and permission errors
• protect the mutating endpoint with the project's request-origin and JSON content-type checks
• add English, Simplified Chinese, and Traditional Chinese translations
• add coverage for API security and creation, path safety, picker behavior/style, current-project initialization, and locale parity

Tests

• node_modules/.bin/tsc --noEmit ✅
• npm run lint ✅
• focused tests: 18 passed ✅
• local HTTP creation smoke test against the development server ✅
• npm test: 1070 passed, 12 failed, 2 skipped. The 12 failures match the pre-existing Windows baseline (path separators, CRLF-sensitive source assertions, model fixture, and native PTY lifecycle tests); this change adds no full-suite failures.

[Ingress007]

Closing at the author's request so the submitted file set can be corrected.