[codex] add zellij run pane adapter

[dapi]

Summary

• Add internal/zellij.Client.RunPane with typed RunPaneRequest, PaneRef, and PaneRunner contract.
• Parse zellij returned pane ids into typed PaneID values and reject non-terminal ids from zellij run.
• Normalize run-pane diagnostics without registry writes and document the FT-016 selected design.

Validation

• mise exec -- go test ./...
• mise exec -- go vet ./...
• python3 scripts/check_memory_bank_index.py
• git diff --check
• rg -n "zelima|Zelima" . (only intentional guidance/glossary matches)
• fresh /review on gpt-5.5 with xhigh: no Critical/High/Important findings; final pass had no Medium/Low code findings

Closes #28