fix(workspace): accept pasted local paths

[chsimonpan]

Summary

• validate pasted workspace directories in the Rust backend instead of the Tauri frontend FS plugin
• import the canonical validated path
• add focused coverage for pasted-path validation and failure handling

Root cause

Paths selected through the native folder dialog receive a runtime filesystem scope grant. Equivalent paths entered directly do not, so frontend plugin-fs.stat() rejected valid pasted directories and reported them as invalid.

Validation

• pnpm exec vitest run src/scaffold/GlobalSpotlight/palettes/WorkspacePalette/pathImport.test.ts
• pnpm run typecheck
• cargo check --manifest-path src-tauri/Cargo.toml -p git (Docker Linux build image)
• pnpm run tauri:build:fast -- --skip-frontend (Docker Linux build image; produced ORG2_1.2.6_amd64.deb)