Refresh installed skills

Re-apply installed channel/provider skills to fetch latest code

Pulling latest skill code without losing local credential wiring or database configuration.

• · list of installed skills (channels+providers)
• · user multiselect of which skills to refresh

• · refreshed skill code files
• · build validation result
• · error summary if apply failed

• · git
• · pnpm build
• · pnpm test

• · working tree is clean
• · upstream channels and providers branches exist

• · dirty working tree blocks preflight
• · upstream branch missing for a skill
• · skill apply script fails during re-fetch

• · idempotent per-skill apply design
• · post-apply validation (build+test)
• · barrel tests assert skill registration