Create a new GitLab issue directly from the widget

[jnwrnr]

User story

As a user, I place a fresh GitJam widget on the board and – instead of pasting an existing URL – choose 'Create new issue' to open a small form and create the issue in GitLab. The card then shows the freshly created issue.

Scope

• Empty-state gains a second primary action: 'Create new issue' beside 'Add GitLab URL'.
• Form fields (in the existing iframe): project path picker (free text first, autocomplete later), title (required), description (multiline), labels (multi-select once we have the labels cache), assignee(s) (autocomplete against project members).
• On submit: POST /projects/:id/issues → card switches into the standard loaded state with the new issue.

Priority

Explicitly lower than editing existing items. Ship after #14 (toggle state) and the other Phase 3 edits.

Acceptance criteria

• New entry point in the empty state.
• Form collects project path, title, description, labels, assignees.
• Successful creation returns the new issue and renders the card.
• PAT must have api scope; friendly error if not.
• Card reference (URL + iid) is cached like any other loaded card.