feat: offer remove workspace on mobile after a merged pull request

[leynier]

Summary

On a merged linked review, the mobile Pull Request action bar now offers Remove Workspace as the primary action, matching desktop #784.

Tapping it runs the existing workspace removal confirmation (showDeleteWorkspaceDialog) and the same cascade / dependency / branch-delete path as the workspace actions sheet. Unlink stays in the overflow. Closed, open, and draft reviews are unchanged.

After a successful removal, the workspace tabs route is popped so the user is back on the workspace list.

No new runtime verbs or protocol version bump. Restack, Watch and Fix, and Ship are out of scope.

Screenshots

No device screenshots. Widget tests cover the merged, closed, no-mutations, confirm-and-delete, and return-to-list paths.

Testing

• Added widget and unit tests for the new action
• flutter test test/pull_request_actions_test.dart (puro Flutter 3.47.2)
• flutter analyze on the touched mobile files
• flutter test test/workspace_panels_test.dart test/workspace_panel_refresh_test.dart test/workspace_list_controller_test.dart

Full-repo format, coverage, and golden suites were not run.

Notes

• This branch does not include feat(mobile): add keep branch option to workspace removal dialog #797 (Keep Branch in the mobile removal dialog). It calls whatever confirmation this worktree already has. When feat(mobile): add keep branch option to workspace removal dialog #797 lands, this path picks it up automatically because both go through confirmAndDeleteWorkspace.
• Docs in docs/architecture.md already describe Remove Workspace on the Pull Request panel after merge; no doc change.
• The mobile delete dialog still uses "Delete Workspace" / "Delete", not the desktop "Remove Workspace?" copy. Rewriting that dialog is feat(mobile): add keep branch option to workspace removal dialog #797, not this PR.

Material risks

• Removal is a destructive runtime action. A failed delete still reports through the existing snackbar path and does not pop the workspace.
• If workspace mutations are unavailable, the button is omitted and unlink remains the only merged action.

[pullfrog]

✅ No new issues found.

Reviewed changes Mobile Pull Request panel after a merged review, matching desktop #784.

• Merged primary action is Remove Workspace (destructive), with Unlink in the overflow; closed, open, and draft reviews stay as they were.
• Mutation gating hides the new action when the paired runtime cannot mutate workspaces, defaulting to offer it until the list answers so Unlink does not flash as primary.
• Shared removal launcher extracts confirmAndDeleteWorkspace from the workspace actions sheet so the panel uses the same confirm, cascade, dependency, and branch-delete path.
• Post-delete navigation pops WorkspaceTabsScreen only after a successful remove; a failed delete snackbars and leaves the workspace open.
• Tests cover the merged default, no-mutations, closed, confirm-before-delete, and return-to-list paths.

  ^{｜ View workflow run ｜ Using Grok ｜ 𝕏}

[pullfrog]

✅ No new issues found.

Reviewed changes Merge of main into this branch since the prior review (ce98a51), which picks up the #797 removal dialog.

• Shared launcher now calls showWorkspaceRemovalDialog and builds a WorkspaceRemovalDecision, including the named-branch canDeleteBranch gate from #797.
• Widget tests assert Remove Workspace? and tap Remove so they match the merged dialog copy.

  ^{｜ View workflow run ｜ Using Grok ｜ 𝕏}