fix: Push preview and RunPod deploy improvements

[akatz-ai]

Summary

• Fix push preview showing "0 commits" when pushing to empty remote
• Disable unsupported RunPod deployment options (Community/Spot)

Changes

Fix: First push to empty remote detection

When pushing to a newly created empty GitHub repository, the push preview incorrectly showed "0 commits to push" because origin/branch doesn't exist yet and the git comparison fails.

Changes:

• Add is_first_push flag to push-preview API response (derived from new remote_branch_exists flag in core library)
• Update PushModal to show "Creating origin/branch with X commits" for first push
• Add info box explaining this will create the remote branch

Note: The core library fix (get_sync_status detecting missing remote branch and counting local commits) is in the comfygit-core package.

Fix: Disable unsupported RunPod options

RunPod doesn't currently support Community cloud type or Spot pricing through our integration.

Changes:

• Disable Community and Spot radio inputs (grayed out at 50% opacity)
• Options remain visible so users know they exist for future support

Test plan

• Create new empty GitHub repo, add as remote, make commit, verify push preview shows correct commit count
• Verify push actually creates the remote branch
• Verify Community and Spot options are visually disabled in RunPod deploy tab