docs: document alias list --json flag and failure-safe conversation caching

[aheritier]

Summary

This PR updates the documentation to reflect two features merged into main in the last 36 hours.

Changes

• docs/features/cli/index.md — Document the --json flag added to docker agent alias list in #2966. Added a --json usage example in the alias usage block, a full JSON output example showing the name/path/options fields, and a note that output is sorted by name and omits false/zero-valued fields.

• docs/features/chat-server/index.md — Document the failure-safe conversation caching behavior fixed in #2947. Added a new "Failure-safe caching" subsection explaining that failed requests (model error, timeout) leave the cached conversation unchanged, clients can safely retry with the same X-Conversation-Id, and transient errors do not corrupt conversation history.

Source PRs covered

Commit	Source PR	What changed
d2de0e1	#2966	alias list --json machine-readable output flag
73f37cf	#2947	Failure-safe conversation cache (failed turns do not corrupt cache)

[docker-agent]

Assessment: 🟢 APPROVE

The documentation additions are accurate and consistent with the PR description. Both the --json flag documentation for docker agent alias list and the failure-safe conversation caching subsection are clear, technically sound, and match the behavior described in the referenced source PRs (#2966 and #2947). No issues found.