Separate Chronicle Skysight into an independent opt-in feature

[joshyorko]

Problem

Chronicle/Skysight activity memory is currently coupled to the broader Record & Replay feature. Users who only want continuous activity-memory resources must enable the recording workflow and share its plugin lifecycle.

Proposed fix

• Add a disabled-by-default chronicle-skysight feature with its own manifest, docs, patch surface, stage and cleanup hooks.
• Stage a restricted MCP plugin exposing only activity-memory tools.
• Make Record & Replay depend on and reuse the shared Skysight backend.
• Keep both features independently selectable and fail closed when the dependency is missing.

The implementation is already exercised in the PatchRaptor fork and is ready to contribute upstream.