Merge pull request #661: feat(config): timestamped config backups with a configurable folder and retention

Conflicts in CLAUDE.md, README.md, docs/api-reference.md and
src/web/server.ts were additions beside #662's Copilot quota read and
#666's keep-warm sections; both sides kept.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/wiki/HTTP-API.md

@@ -173,6 +173,10 @@ curl -s "$API/api/subagents" | jq                  # background agents
 curl -s "$API/api/search?q=deploy" | jq            # cross-session search
 curl -s "$API/api/mcp-sync" | jq                    # preview MCP server sync (opt-in: 403 until mcpSyncEnabled is on)
 curl -s -X POST "$API/api/mcp-sync" | jq             # apply it: add missing servers to each CLI config, never edit/remove
+curl -s "$API/api/config-backups" | jq              # config snapshots: folder, retention, list (admin only in multi-user mode)
+curl -s -X POST "$API/api/config-backups" | jq      # back up the customized config files now
+curl -s -X POST "$API/api/config-backups/cfg-20261011-120000/restore" | jq   # put a snapshot back (after a pre-restore copy)
+curl -s "$API/api/config-backups/diff?from=cfg-20261011-120000" | jq   # what differs from the running config (`to=` another snapshot id to compare two)
 
 # with ID set to a session id:
 curl -s "$API/api/sessions/$ID/last-response" | jq -r '.data.text'   # last answer, from the transcript (claude, codex, deepseek)