fix(scheduled): pause bound tasks when removing a project

[hui455]

Removing a project leaves its scheduled tasks enabled. A later automatic run can recreate the project and a conversation after the user has removed it.

Pause the project's tasks while preserving their definitions, bindings and run history. An admitted run blocks removal even before its conversation opens a turn. Other projects are unaffected. An explicit Resume or Run now can still use the saved path; deleting project conversations may remove their links from the retained history.

Before and after — actual Windows desktop after removing the project (1200 × 800, isolated profiles).

Before:

After:

Regression tests reproduce automatic project recreation and cover admission before a turn, task/history retention, project isolation and restart.

Validation details

• Project-removal regressions and real Host admission/removal/restart E2E passed. The Manual-to-Hourly compatibility E2E passed.
• Scheduled Rust suite: 21 passed, 4 existing Windows path assertion failures, addressed by the separate workspace-path fix.
• Formatting and diff checks passed.
• Windows, Node 24.2, Rust debug build. Native macOS/Linux runs were not performed. Screenshots use main 0111e306c and the corresponding fix; focused checks were rerun after refreshing the candidates to 46d4ee4ee.

[vastsa]

Landing note: this branch conflicted with the sibling scheduled-task PRs (#820-#824) that landed just before it. I merged the updated main into this branch and resolved the conflicts (docs sections unioned; for #822 the new tests in scheduled_tools.rs were combined with #820's). No functional change was made to your commits.