Add bounded Editor log diagnostics

[niqibiao]

Summary

• add read-only editor/console.get(afterMarkerId="")
• read a stable Editor log snapshot without changing Unity Console UI state
• cap resultJson at 16 KiB and fail closed when a causal marker is unavailable
• centralize marker formatting/path resolution and harden marker labels

This PR is stacked on codex/at-most-once-protocol so it stays separate from the reliability protocol work.

Validation

• 35/35 console-client core tests
• 208/208 REPL tests
• Unity 2022 package refresh and live command discovery
• live clean-window, post-marker, missing-marker, invalid-label, reload, and truncation probes

Companion

Companion unity-cli contract: niqibiao/unity-cli-skill#14