Reload projects changed on disk - #46

One-line description

Reload a project in the desktop app when its file changes on disk, and ask first when there are unsaved changes.

This allows you to keep a model open while an LLM agent works on it in paralell. When changes are detected, the app asks if you want to reload from disk or override.

Changes in detail

• A clean project reloads from disk and keeps the current camera. Unsaved changes show a prompt with "Keep my changes" and "Reload from disk".
• The file is checked about once a second while the app is idle. A change needs a new modification stamp and different content, so touching a file or rewriting identical bytes does nothing.
• A reload waits until a viewport gesture, modeling or text/rename edit finishes.
• A reload that reads a partly written file keeps the current document and retries on the next change.
• A reload does not reorder Recent Projects.
• Desktop only. The web build is unchanged.
• Useful alongside tools that edit .bup files externally.

Testing

• Seven new tests in project_tests.rs: reload of a clean project, prompt with unsaved changes, own save not reloading, unreadable write retry, one-second check interval, same-content rewrite ignored, and deferral during a viewport drag.
• Ran the benchup-app library tests on this commit: all 27 project tests pass, and the branch adds no failures compared with main.
• cargo check for wasm32-unknown-unknown is free of warnings.