feat: add AI-powered Quick Push workflow

[markwylde]

Summary

• Adds a Quick Push mode to the git push context menu (⚡ button) that uses the configured AI provider to auto-generate commit messages, branch names, and PR details from the current working-tree diff
• Introduces a reusable trailing action button on context menu rows to surface the new entry point without cluttering the primary action
• Implements the full electron-side service (QuickPushService) that calls AiTabMetadataService.runPrompt, parses the model's JSON plan, and runs the git operations (stage → commit → push → optional PR)

Test plan

• Open a project with staged/unstaged changes, right-click the git push button, and verify the ⚡ icon appears next to each action
• Click ⚡ without an AI provider configured — confirm the settings modal opens with the correct section
• With a provider configured, trigger Quick Push and verify the review modal shows branch name, commits, and file lists
• Approve the plan and confirm commits land on the correct branch and a PR is created when requested
• Verify cancelling mid-review (Escape / Cancel) does not leave any partial git state