fix: improve grok-local skill compatibility for image edit and proxy setup

[double2tea]

Context

• A local grok-local skill was built in the paired skill workspace (~/.config/skillshare/skills/grok-local) to call grok2api for chat/search/image/video/image-edit flows.
• During integration, two blockers were found on the grok2api side: image-edit render-card parsing gaps and proxy/CA trust issues in local docker setups.

Summary

• Improve image_edit response handling for grok-local workflows by parsing render-card outputs (cardAttachmentsJson + <grok:render> mappings) in addition to direct image URLs.
• Normalize image conversion in one path (url or base64) to reduce empty-result responses during local image-edit usage.
• Improve local container reliability for proxy-heavy environments by clearing injected proxy vars in compose and loading custom CA certs from data/certs/*.crt at startup.

Why this PR is in this repo

• The skill itself lives outside this repository, but it depends on grok2api behavior.
• This PR contains the upstream service-side fixes required for that skill to work reliably in local environments.

Test Plan

• Manual integration verification on local grok2api + grok-local workflows (image-edit, video-related retry paths).
• pytest tests/test_grok_local.py tests/test_skill_metadata.py in the paired local skill workspace.

[double2tea]

Closing per author request.