Publish source package

[luojiang419]

What changed

• Publishes the current source package for the Canvas desktop/backend work.
• Adds backend support modules, tests, Tauri desktop source/configuration, portable build scripts, and new static workbench pages.
• Adds a .gitignore to keep dependencies, build outputs, local runtime data, backups, generated schemas, and sensitive local docs out of source control.
• Removes obsolete local workflow/static pages that are no longer part of this source package.

Validation

• python -m pytest tests passed: 69 tests.
• npm run desktop:build passed and produced the Tauri executable locally.

Notes

Direct push to hero8152/Infinite-Canvas was denied for the authenticated account, so this branch was pushed from the fork luojiang419/Infinite-Canvas.