fix(desktop): close tabs when removing workspace to prevent ghost reappear

[HUQIANTAO]

Problem

Removed workspaces reappear in the sidebar every time the application restarts.

Reproduction (Issue #5079):

1. Open a project workspace in a tab
2. Right-click the project in the sidebar and select "Remove from sidebar"
3. Close and relaunch Reasonix
4. The removed project reappears in the sidebar

Root Cause

Three persistence layers are involved:

File	Purpose
desktop-projects.json	Project list with topics
desktop-workspaces.json	Legacy workspace list
desktop-tabs.json	Open tabs with workspaceRoot and topicId

RemoveWorkspace (desktop/app.go:1121) only cleaned up the first two:

forgetWorkspace(dir)       → removes from desktop-workspaces.json
removeProject(dir)         → removes from desktop-projects.json
// desktop-tabs.json is NOT cleaned up

On shutdown, saveTabsLocked() persisted the still-open tabs (with their WorkspaceRoot pointing to the removed workspace) back to desktop-tabs.json. On the next startup:

1. restoreOrBuildTabs reads desktop-tabs.json and creates tabs for the removed workspace
2. buildTabController calls ensureTopicIndexed (desktop/tabs.go:1364)
3. ensureTopicIndexed unconditionally re-adds the project to desktop-projects.json if not present
4. The removed workspace reappears in the sidebar

Fix

Close all tabs belonging to the workspace before removing it from the project index. This follows the same pattern used by TrashTopic (desktop/tabs.go:1937):

1. Collect all tabs where WorkspaceRoot == dir
2. Snapshot and close each tab's controller
3. Remove tabs from a.tabs and a.tabOrder
4. Handle active tab selection if the removed tab was active
5. Create a fallback global tab if all tabs were removed
6. Call saveTabsLocked() to persist the cleaned state

Then proceed with the existing forgetWorkspace + removeProject cleanup.

Changes in desktop/app.go:

func (a *App) RemoveWorkspace(dir string) error {
    if dir == "" {
        return fmt.Errorf("workspace path is required")
    }
    dir = normalizeProjectRoot(dir)

+   // Close all tabs belonging to this workspace so that saveTabsLocked does
+   // not persist them. On the next startup restoreOrBuildTabs would otherwise
+   // re-create the tabs and ensureTopicIndexed would re-add the project to
+   // desktop-projects.json, making the removed workspace reappear.
+   a.mu.RLock()
+   var workspaceTabs []*WorkspaceTab
+   for _, tab := range a.tabs {
+       if tab.WorkspaceRoot == dir {
+           workspaceTabs = append(workspaceTabs, tab)
+       }
+   }
+   a.mu.RUnlock()
+
+   for _, tab := range workspaceTabs {
+       if tab.Ctrl != nil {
+           tab.Ctrl.Snapshot()
+           tab.Ctrl.Close()
+       }
+       if tab.sink != nil {
+           tab.sink.ctx = nil
+       }
+   }
+
+   if len(workspaceTabs) > 0 {
+       a.mu.Lock()
+       removedActive := false
+       for _, tab := range workspaceTabs {
+           if a.tabs[tab.ID] != tab { continue }
+           if a.activeTabID == tab.ID { removedActive = true }
+           delete(a.tabs, tab.ID)
+           a.removeTabOrderLocked(tab.ID)
+       }
+       if removedActive {
+           a.activeTabID = ""
+           if len(a.tabOrder) > 0 { a.activeTabID = a.tabOrder[0] }
+       }
+       if len(a.tabs) == 0 {
+           a.mu.Unlock()
+           a.OpenGlobalTab("")
+           a.mu.Lock()
+       }
+       a.saveTabsLocked()
+       a.mu.Unlock()
+   }

    forgetWorkspace(dir)
    if err := removeProject(dir); err != nil {
        return err
    }
    a.emitProjectTreeChanged()
    return nil
}

Testing

1. Open a project workspace in one or more tabs
2. Remove the workspace from the sidebar
3. Verify all tabs for that workspace are closed
4. Verify a fallback tab is created if no tabs remain
5. Restart the application
6. Verify the removed workspace does not reappear in the sidebar
7. Verify remaining workspaces and their tabs are unaffected