feat: add pane pid session evidence

[dapi]

Summary

• Add optional PID-correlated Codex session evidence as a final sessions detect fallback after command evidence and indexed session_meta lookup fail.
• Parse transient pane PID fields from zellij JSON and pass them through a resolver boundary without persisting PID/raw argv/env/process details.
• Extend sessions detect --explain with redacted PID fallback verdict/source/reason fields while keeping default output unchanged.
• Document the selected FT-046 adapter boundary and privacy rules.

Fixes #84

Checks

• rg --files memory-bank
• python3 scripts/check_memory_bank_index.py
• git diff --check
• rg -n "zelima|Zelima" . (only existing instruction/glossary references)
• docker run --rm -v "$PWD:/work" -w /work golang:1.25 sh -lc '/usr/local/go/bin/gofmt -w internal/codex/session_evidence.go internal/codex/session_evidence_test.go internal/zellij/parse.go internal/zellij/parse_test.go internal/detection/detect.go internal/detection/detect_test.go internal/cli/cli.go internal/cli/cli_test.go && /usr/local/go/bin/go test ./internal/codex ./internal/zellij ./internal/detection ./internal/cli'\n- docker run --rm -v "$PWD:/work" -w /work golang:1.25 sh -lc '/usr/local/go/bin/go test ./...'\n\n## Notes\n\nLocal host PATH does not include Go; Go checks were run in the golang:1.25 Docker image with /usr/local/go/bin/go and /usr/local/go/bin/gofmt.\n