feat: delete a worktree from the Space actions menu

[kbwo]

Why

Deleting a worktree required the D screen, which lists every worktree and makes you locate the one that is already highlighted in the menu. Space now opens the row actions for the highlighted worktree and can delete it directly.

What changed

• Space works on any worktree row, not only rows that have a session. Rename/Close are session-specific and stay hidden when the row has no session, so the menu title switches to "Worktree Actions".
• The delete entry is hidden when the worktree cannot be deleted (the main worktree, and the worktree containing the current working directory) instead of being shown and rejected. That rule moved into isDeletableWorktree() in src/utils/worktreeUtils.ts, and the existing D screen now uses it too, so both paths share one source.
• Choosing it reuses the existing confirmation and deletion path: DeleteConfirmation (uncommitted-changes warning, branch option, Cancel selected by default) followed by handleDeleteWorktrees, which kills the worktree's sessions before removing it. On failure this flow returns to the menu with the error, because the multi-select delete screen was never opened here.
• The Dashboard entry point into the actions menu has only a session and no worktree, so it offers no deletion.

MenuAction.sessionActions now carries the Worktree instead of a bare worktreePath (the path is read from it, so the two no longer duplicate each other).

Verification

• bun run lint, bun run typecheck: pass.
• bun run test: 1788 passed. The *.submodule.test.ts files fail in beforeAll in my local environment because git config --global protocol.file.allow always cannot write ~/.gitconfig there; this is unrelated to the change (the prebuilt, unmodified dist copies of those tests fail identically). CI should run them normally.
• New tests: src/components/SessionActions.test.tsx (which entries are offered, hotkey dispatch), a Menu.test.tsx case for Space on a session-less row, and isDeletableWorktree cases in src/utils/worktreeUtils.test.ts.
• Not verified by driving the actual TUI.

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