fix: make Space and Project deletion permanent

[xdCloudy]

Related Issue

Fixes #1793

Description

Deleting a Project currently removes its task/history state from the UI but can leave the durable Project row behind. Deleting a Space then fails with space_has_projects, even though the Space deletion confirmation says the Space and all of its Projects will be permanently deleted.

This change makes the destructive actions match that UI contract.

Root cause

• SpaceService.delete_space() rejects any Space that still has Project rows, including archived Projects.
• deleting the final ChatHistory removes triggers but does not remove the durable Project row.
• Project deletion can fan multiple history DELETE requests out in parallel, so final-history cleanup needs to serialize per Project.

Changes

• add a shared deletion service for Project/Space dependent rows
• remove the durable Project when its final history is deleted
• serialize concurrent history deletion on the Project row
• make Space deletion cascade through contained Projects
• add DELETE /spaces/{space_id}/projects/{project_id} for direct Project deletion
• keep ownership checks on both Project and Space deletion
• add regression tests covering Project deletion, Space cascade deletion, and ownership isolation

The cleanup covers chat histories, trigger executions/triggers, Project/Space memory, pending file overlays, and Space file-index rows before removing the parent records.

Testing

Regression tests are included in server/tests/test_space_project_deletion.py for:

• deleting a Project while preserving its parent Space
• deleting a Space together with its Projects and Space-scoped data
• refusing to delete a Project owned by another user

Manual reproduction was on Windows: Project deletion appeared to succeed in the UI, but the remaining server Project row caused subsequent Space deletion to fail. This PR is currently a draft pending branch test/CI results.

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Contribution Guidelines Acknowledgement

• I have read and agree to the Eigent Contribution Guideline.