feat(frontend): enhance the workflow error panel display

[marrouchi]

What changed?

Improves the blocking overlay shown when a workflow can't be compiled, making a long list of issues easier to scan and act on.

Changes

• Header: icon now sits in a tinted badge, with a one-line hint ("Fix the issues below in the YAML editor…") and an issue-count pill so the scope reads at a glance.
• Issue list: each issue is now a bordered card with a dot marker instead of a flat list, keeping each Line N jump chip tied to its message.
• Affordances: Line N chips get a solid surface + hover border; the "Open YAML editor" CTA gains a trailing arrow and hover transitions.
• i18n: added invalid_workflow_hint and pluralized issue_count keys (en + fr).

All colors derive from the existing --workflow-error-* tokens via color-mix, so light and dark themes work with no new variables. Purely presentational — no behavior or overlay-semantics changes.

[yassinedorbozgithub]

LGTM ✅

These enhancements improve error handling by providing better organization, clearer structure, and a more intuitive experience for users.

• After the enhancement

• Before the enhancement