🤖 fix: add sidebar variant delete-all menu

[coadler]

Summary

Adds bulk-delete actions for sidebar variant groups and fixes the Nix dev shell/static formatting path so local validation includes the required formatter/linkcheck tools.

Background

Variant task groups were collapsed into a single sidebar row, but deleting the whole set required expanding the group and deleting variants one by one. While validating the change, the Nix dev shell could not evaluate because current nixpkgs removed mdbook-linkcheck, and fmt-nix-check attempted to run nix fmt from a temp directory without flake metadata.

Implementation

• Adds a hover/focus 3-dot action menu to variant group rows, with the same right-click/long-press context menu behavior used elsewhere in the sidebar.
• Adds a destructive “Delete all variants” confirmation and force-removes every workspace in the variant group.
• Tracks in-flight group deletion and surfaces deletion failures through the existing popover error path.
• Replaces the removed mdbook-linkcheck package with mdbook-linkcheck2 in the dev shell.
• Updates Nix formatting checks to run against the repo flake with nix fmt -- --check flake.nix instead of evaluating a temp-copy flake.

Validation

• bun test src/browser/components/ProjectSidebar/ProjectSidebar.test.tsx
• nix develop --command make fmt-check
• nix develop --command make static-check

Risks

Low-to-medium risk. The UI change is scoped to coalesced variant group rows and uses the existing workspace removal path, but deleting a full variant group is destructive by design and relies on the existing confirmation/force-delete behavior.

---

Generated with mux • Model: openai:gpt-5.5 • Thinking: xhigh • Cost: $0.00

[coadler]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Already looking forward to the next diff.

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[coadler]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. More of your lovely PRs please.

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".